B.  A.  RUDOLPH 


UNIVERSITY    OF   CALIFORNIA 

COLLEGE   OF   AGRICULTURE 

AGRICULTURAL    EXPERIMENT   STATION 

BERKELEY,    CALIFORNIA 


Co 

Reserve 

AVOCADO  CULTURE  IN  CALIFORNIA 


PART  I.     History,  Culture,  Varieties,  and  Marketing 
KNOWLES  A.  RYERSON 

PART  II.     Composition  and  Food  Value 
M.  E.  JAFFA  and  H.  GOSS 

revision  by  R.  W.  HODGSON 


BULLETIN  365 

June,  1923 

Reprinted  December,  1924 

Eevised  June,  1928 


UNIVERSITY  OF  CALIFORNIA  PRINTING  OFFICE 

BERKELEY,  CALIFORNIA 

1928 


FOREWORD 

The  rapid  growth  of  the  avocado  industry  has  been  one  of  the 
notable  developments  in  California  horticulture  during  the  past 
fifteen  years.  This  period  has  witnessed  a  transition  in  the  use  of 
the  avocado  from  that  of  a  dooryard  curiosity  to  a  fruit  supporting 
a  well  established  commercial  industry  embracing  approximately  four 
thousand  acres.  The  first  publication  on  the  avocado  issued  by  the 
College  of  Agriculture  appeared  in  1915  in  response  to  the  need 
expressed  at  that  time.  The  information  then  available  was  necessarily 
limited ;  the  industry  has  made  rapid  strides  since  its  publication ; 
methods  and  practices  have  changed;  and  much  new  information  has 
been  developed.  In  order  to  meet  the  rapidly  growing  demand  for 
the  best  information  available  Bulletin  365  was  prepared  and  issued 
in  1923.  This  publication  has  now  run  through  two  issues  and  in 
order  to  bring  it  up  to  date  has  been  completely  revised  in  this  print- 
ing. The  material  referring  to  methods,  practices  and  varieties  must 
be  considered  in  relation  to  a  young,  rapidly-growing  industry,  which 
has  been  little  investigated,  hence  the  information  furnished  will  be 
subject  to  further  modification  as  progress  is  made. 

Robert  W.  Hodgson, 
Division  of  Subtropical  Horticulture. 


Digitized  by  the  Internet  Archive 

in  2012  with  funding  from 

University  of  California,  Davis  Libraries 


http://www.archive.org/details/avocadocultur3651928berk 


HISTORY,  CULTURE,  VARIETIES,  AND  MARKETING 

PART  I 

KNOWLES  A.  RYERSON 


HISTORY 

The  first  reference  to  the  introduction  of  the  avocado  into  Cali- 
fornia is  made  in  the  Report  of  the  Visiting  Committee  of  the 
California  State  Agricultural  Society  in  1856.  According  to  this 
report  Dr.  Thomas  J.  White,  living  near  San  Gabriel,  had  imported 
the  avocado  from  Nicaragua  along  with  other  tropical  fruit  plants. 
It  was  not  until  some  years  later  that  the  avocado  became  definitely 
established  through  the  introduction  of  three  trees  from  Mexico  in 
1871  by  Judge  R.  B.  Ord  of  Santa  Barbara.  Two  of  the  three  trees 
of  his  importation  for  many  years  bore  fruit  in  Santa  Barbara  and 
served  to  create  interest  in  further  plantings. 

California  has  been  fortunate  in  having  had  among  her  early 
settlers  persons  who  have  taken  a  keen  interest  in  horticulture, 
especially  that  phase  of  it  dealing  with  subtropical  plants — fruit- 
bearing  and  ornamental.  The  early  history  of  the  avocado  in  this 
state  is  particularly  marked  by  such  effort.  In  the  years  following  the 
introduction  by  Judge  Ord,  many  trees  were  planted,  some  being 
imported  from  Mexico  and  the  countries  of  Central  America,  others 
being  started  from  the  seeds  of  the  many  fruits  that  had  found  their 
way  into  California,  brought  here  by  travelers.  Among  the  many 
who  contributed  much  to  the  impetus  given  avocado  growing  were 
Mr.  J.  C.  Harvey  and  Dr.  F.  Franceschi  (Fenzi),  formerly  of  Santa 
Barbara. 

In  the  early  nineties  Mr.  Juan  Murrieta,  becoming  interested  in 
the  avocado  through  Mr.  Harvey,  imported  a  considerable  quantity 
of  thick  skinned  fruits  from  Atlixco,  Mexico.  Some  seeds  from  these 
he  distributed  among  his  friends  and  others  he  planted.  From  this 
group  of  seedling  trees  have  come  a  number  of  the  varieties  that  first 
attracted  attention,  as  promising  commercial  fruits,  fifteen  to  eighteen 
years  ago.  These  include  the  Royal,  Walker,  Challenge,  Dickey, 
Blakeman,  Sharpless,  Colorado  and  Murrieta.  Mr.  C.  P.  Taft  of 
Orange,  in  1899  and  the  years  immediately  following,  also  planted 
many  seeds  from  various  sources.     As  a  result  of  the  showing  made 


6 


UNIVERSITY  OF  CALIFORNIA EXPERIMENT  STATION 


by  the  fruits  produced  in  the  plantings  mentioned,  interest  in  the 
commercial  possibilities  of  the  avocado  received  a  decided  impetus  in 
1911  and  1912. 

The  period  since,  has  been  marked  by  special  emphasis  on  the 
commercial  aspects  of  avocado  culture  (fig.  1).  In  place  of  relying 
on  chance  seedlings,  nurserymen  began  the  exploration  of  the  avocado 
districts  of  Mexico  and  Guatemala.  F.  0.  Popenoe  and  T.  U.  Barber 
of  the  West  India  Gardens,  Altadena,  were  pioneers  in  this  field,  and 


Fig.  1. — Bearing  avocado  orchard  in  southern  California. 

during  1911-12  brought  in  buds  from  many  varieties  in  the  best  dis- 
tricts of  Mexico.  Of  these  the  Fuerte  and  Puebla  have  proved  to  be 
of  especial  merit.  E.  E.  Knight  of  Yorba  Linda,  a  resident  for  many 
years  in  Central  America,  brought  in  buds  of  superior  varieties  from 
Guatemala,  of  which  the  Queen  and  Linda  are  the  most  promising. 

Mr.  Joseph  Sexton  of  Goleta,  imported  selected  seed  and  buds 
from  the  best  West  Indian  varieties  grown  in  the  Hawaiian  Islands. 
The  failure  of  his  planting,  under  favorable  climatic  conditions,  early 
indicated  the  futility  of  planting  varieties  of  this  race.  Realizing, 
however,  that  private  endeavor  could  not  expect  to  cover  completely 
the  avocado  districts  of  foreign  countries,  and  that  thorough  investi- 


"BUL.  365]  AVOCADO  CULTURE  IN  CALIFORNIA  7 

gation  should  be  made  in  such  places  if  the  industry  was  to  start  out 
with  the  advantage  of  the  best  varieties  available  as  a  foundation,  the 
U.  S.  Department  of  Agriculture  undertook  the  exploration  of  all 
avocado  districts  in  Mexico  and  Central  and  South  America.  For  the 
better  part  of  nine  years  Dr.  Wilson  Popenoe,  as  an  agricultural 
explorer,  combed  these  regions,  with  the  result  that  the  avocado 
growers  of  California  and  of  Florida  now  have  the  best  that  the 
world  affords  in  the  way  of  varieties  upon  which  to  built  a  commercial 
industry.  Probably  no  other  horticultural  industry  has  had  a  similar 
advantage  in  its  infancy.  These  introductions  have  now  been  under 
test  for  a  number  of  years  and  some  of  them  are  showing  decided 
promise  in  southern  California.  It  will  require  several  years  more 
at  least  before  their  value  and  adaptation  to  conditions  in  this  state 
will  be  determined. 

The  work  of  the  California  Avocado  Association,  which  was 
organized  in  1914,  has  been  one  of  the  important  factors  in  the  rapid 
development  of  avocado  culture.  Its  Committee  on  Registration  and 
Classification  of  Varieties  has  rendered  particular  service  in  studying 
varieties  and  recommending  those  suitable  for  commercial  planting; 
its  present  list  of  a  few  standard  varieties  is  an  indication  of  the 
careful  work  which  has  characterized  its  activities.  The  published 
proceedings  of  this  organization  form  the  most  valuable  contribution 
to  avocado  literature  available  at  the  present  time. 

Fostered  by  the  Association,  a  cooperating  marketing  agency,  the 
California  Avocado  Growers'  Exchange,  was  formed  in  1924  and  thus 
far  it  has  functioned  successfully  in  marketing  the  rapidly  increasing 
crop.    In  1927  the  name  was  changed  to  Calavo  Growers  of  California. 


BOTANICAL   DESCRIPTIONS   AND    RELATIONS 

The  avocado  belongs  to  the  genus  Persea,  a  member  of  the  Laurel 
family,  to  which  belong  also  such  economic  plants  as  camphor,  sassa- 
fras and  cinnamon.  The  common  native  California  bay  tree  is  like- 
wise a  member  of  this  family.  The  cultivated  species  of  this  genus 
are  native  to  Mexico,  Central  and  South  America.  Early  classification 
of  avocados  cultivated  in  the  United  States  placed  all  in  one  genus, 
Persea  americana  Mill,  (P.  gratissima  Gaertn.)  Later  studies  have 
revealed  two  distinct  species,  P.  americana  and  P.  drymifalia;  the 
former  includes  all  varieties  horticulturally  grouped  in  the  West 
Indian  and  Guatemalan  races;  the  latter  includes  the  small  fruited 
varieties  of  the  Mexican  highlands,  of  which  many  are  grown  in 


8  UNIVERSITY  OF  CALIFORNIA EXPERIMENT  STATION 

California,  and  which  have  also  spread  to  Ecuador,  Chile,  and  to  a 
limited  extent  to  the  regions  bordering  the  Mediterranean.  These  are 
grouped  into  the  so-called  Mexican  race. 

Persea  drymifolia  can  be  distinguished  from  P.  americana  by  the 
very  pronounced  anise  odor  that  can  be  detected  in  the  leaves  and 
young  growth  of  the  former  when  crushed ;  this  odor  is  entirely  lack- 
ing in  P.  americana.  The  flowers  of  P.  drymifolia  are  regularly  more 
pubescent  than  those  of  P.  americana  and  the  under  surface  of  the 
leaves  more  glaucous.  The  fruits  of  P.  drymifolia  are  characterized 
by  a  thin,  membranous  skin,  differentiating  them  markedly  from  those 
of  P.  americana  which  have  a  thick  skin  varying  from  a  leathery  to  a 
brittle  texture.  The  fruits  of  the  latter  species  are  usually  much 
larger  than  those  of  the  former.  Both  species  are  represented  in  the 
cultivated  avocados  of  California. 

The  tree  is  evergreen,  though  in  certain  varieties  practically  all  of 
the  leaves  drop  for  a  brief  period  during  the  flowering  season.  The 
leaf  blades  are  of  many  different  shapes — oval,  ovate,  obovate,  lance- 
olate, elliptic ;  and  combinations  of  these  appear.  The  leaf  base  is 
usually  acute  or  truncate,  the  apex  varies  from  almost  blunt  to 
acuminate.  In  length  the  leaves  vary  from  3  to  15  inches.  The  color 
of  the  mature  foliage  is  usually  bright  green,  the  young  growth,  how- 
ever, often  exhibits  varying  shades  of  red  and  bronze.  The  manner  of 
three  growth  is  variable,  the  tall,  upright,  unbranched  habit  and  the 
short,  well-shaped,  spreading  habit  are  both  commonly  found.  Seedling 
trees  attaining  an  extreme  height  of  from  fifty  to  sixty  feet  have  been 
noted  where  soil  conditions  are  particularly  favorable  (fig.  2).  Bud- 
ding apparently  has  a  dwarfing  effect.  The  resulting  trees  are  more 
compact  and  spreading,  and  seemingly  not  inclined  to  grow  as  high  as 
seedlings.    None  are  of  sufficient  age  however  to  settle  this  definitely. 

The  small,  pale,  green  or  yellowish  flowers  are  borne  in  terminal 
racemes.  They  possess  both  stamens  and  pistil.  Differentiation 
between  calyx  and  corolla  does  not  occur  in  the  avocado  blossom.  The 
petal-like  structures  are  in  reality  perianth  lobes,  of  about  equal 
length,  the  inner  series  sometimes  being  longer  than  the  outer.  They 
are  more  or  less  pubescent,  pronouncedly  so  in  Persea  drymifolia  and 
sometimes  almost  glaucous  in  P.  americana.  The  nine  stamens  are 
arranged  in  three  series ;  the  anthers  are  four-called,  the  cells  opening 
by  valves  hinged  at  the  upper  end.  At  the  base  of  each  stamen  of  the 
inner  series  are  two  large,  orange  colored  glands  which  secrete  nectar, 
presumably  for  the  attraction  of  insects.  Inside  the  stamens  are  three 
staminodia.    The  ovary  is  one-celled,  and  contains  a  single  ovule.    The 


Bul.  365] 


AVOCADO   CULTURE  IN   CALIFORNIA 


Fig.  2. — Mature  seedling  avocado  tree  indicating  the  height  to  which  such  trees 
grow  in  southern  California.     Note  also  the  lath  screen  for  wind  protection. 


10  UNIVERSITY  OF  CALIFORNIA — EXPERIMENT  STATION 

style  is  slender,  usually  hairy,  with  a  simple  stigma.  The  flowers 
appear  from  November  to  May  in  California,  varying  according  to 
variety  and  locality. 

The  fruit  of  the  cultivated  species  is  extremely  variable  in  size, 
shape,  color  and  other  characters.  Fruits  of  Persea  drymifolia  are 
found  that  are  no  larger  than  good  sized  olives,  while  the  largest 
varieties  of  P.  americana  weigh  over  three  pounds.  In  shape  they 
may  be  round,  oval,  pyriform,  "bottle  necked,"  or  any  of  the 
numerous  gradations  between  these  forms.  The  color  ranges  from 
light,  yellowish  green,  through  dark  green,  maroon,  brown,  reddish 
brown  to  purplish-black.  The  skin  is  thin  and  membranous  in 
P.  drymifolia,  while  in  P.  americana  it  is  thick,  tough,  and  even 
woody,  or  shell-like  in  some  varieties,  with  an  extreme  thickness  of  a 
quarter  of  an  inch.  The  fleshy,  edible  part,  lying  between  the  skin 
and  the  single  large  seed,  is  of  a  buttery  consistency,  creamy  to  bright 
yellow  in  color,  often  greenish  near  the  skin.  It  contains  a  high 
percentage  of  oil.  Streaks  of  fine  fibers  traverse  the  flesh  from  the 
stem  to  the  base  of  the  seed;  these  make  up  the  vascular  system,  and 
are  invisible  in  ripe  fruits  of  many  varieties.  Each  fruit  contains  a 
single,  large  seed,  and  the  seeds  of  different  varieties  vary  greatly  in 
shape,  being  round,  oblate,  spherical,  conical,  or  of  slender  form. 
The  seed  is  inverted  in  the  fruit  so  that  the  base  is  on  the  side  away 
from  the  stem  and  is  covered  by  two  seed  coats  of  varying  thickness, 
often  adhering  closely  to  one  another.  The  cotyledons  are  normally 
two,  sometimes  three  in  P.  drymifolia,  white  or  greenish  white  in  color, 
and  smooth  or  roughened  on  the  surface.  The  seed  is  tight  in  the 
cavity  in  some  varieties  and  loose  in  others. 


AVOCADO  DISTRICTS  IN  CALIFORNIA 

The  commercial  avocado  plantings  of  the  state  are  located  in 
climatically  favored  areas  in  southern  California  in  two  more  or  less 
clearly  defined  districts.  The  first  is  strictly  coastal,  embracing 
Ventura,  Santa  Barbara  and  parts  of  Orange,  Los  Angeles,  and  San 
Diego  counties,  and  is  subject  to  direct  ocean  influence.  The  second 
general  district  embraces  the  foothill  slopes  of  the  San  Fernando,  San 
Gabriel,  and  Santa  Ana  valleys,  including  Pasadena,  Monrovia, 
Duarte,  Uplands,  Redlands,  Riverside,  and  North  Whittier  Heights. 
In  between  these  two  general  regions  lie  intermediate  districts  such 
as  Fillmore,  Hollywood,  Whittier,  and  La  Habra  which  partake  of 
the  characteristics  of  both.    The  plantings  are  for  the  most  part  con- 


BUL.  365]  AVOCADO  CULTURE  IN   CALIFORNIA  11 

fined  to  the  warmer  parts  of  the  citrus  belt.  Plantings  in  the 
Coachella  and  Imperial  valleys  have  proved  unsuccessful  probably 
because  of  the  extreme  atmospheric  dryness  and  the  intense  heat. 

The  avocado  has  been  planted  in  central  and  northern  California 
in  many  scattered  localities.  Trees  are  fruiting  in  Fresno,  Tulare, 
Butte  and  other  counties,  and  in  sheltered  locations  in  the  San 
Francisco  Bay  region.  They  are  for  the  most  part  Mexican  seedlings 
and  indicate  that  commercial  varieties  may  be  developed  for 
these  sections.  Commercial  plantings  in  these  districts  are  still 
experimental. 

California  is  justifiably  noted  for  remarkable  variation  and 
diversity  of  climatic  and  soil  conditions  within  relatively  small  areas. 
The  success  of  a  crop  on  a  given  site  is  therefore  by  no  means  a  safe 
criterion  on  which  to  predict  the  success  of  the  same  crop  on  areas 
close  by.  This  fact  is  especially  important  in  its  application  to  the 
selection  of  land  for  avocado  plantings,  on  account  of  the  extreme 
sensitiveness  of  this  fruit  to  unfavorable  environmental  conditions. 
Thus,  in  the  commercial  areas  above  mentioned,  by  no  means  all  of 
the  land  is  adapted  to  avocado  culture.  In  selecting  a  site  for  an 
avocado  orchard  it  is,  therefore,  highly  important  that  accurate 
information  be  obtained  as  to  climatic  and  soil  conditions.  It  is 
certain  that  many  of  the  avocado  plantings  made  in  recent  years 
are  likely  to  prove  unsuccessful  on  account  of  unfavorable  environ- 
mental conditions.  Information  concerning  climatic  conditions,  and 
particularly  the  frost  hazard,  may  be  obtained  from  representatives 
of  the  United  States  Weather  Bureau.  Data  bearing  on  soil  conditions 
are  available  in  the  various  soil  survey  reports.  Intending  avocado 
planters  are  advised  to  consult  the  County  Farm  Advisor  before 
selecting  the  site  for  the  orchard. 


CLIMATIC    REQUIREMENTS 

In  general,  the  avocado  is  similar  to  the  citrus  fruits  in  its  climatic 
requirements.  The  Mexican  race  can  be  grown  where  the  orange 
thrives,  while  the  more  tender  Guatemalan  race  is  adapted  to  the 
milder  districts  best  suited  to  lemon  growing.  Beyond  a  doubt  the 
primary  limiting  factor  of  commercial  avocado  growing  is  the  occur- 
rence of  low  winter  temperatures.  The  relative  importance  of  this 
factor  is  directly  dependent  upon  the  degree  and  duration  of  such 
temperatures.  Observations  made  following  the  cold  waves  of  1913, 
1917,  1922  and  1925  have  served  to  verify  these  conclusions.     The 


12  UNIVERSITY  OF  CALIFORNIA EXPERIMENT  STATION 

summary  here  quoted,  made  by  Webber1  following  the  winter  of  1916- 
1917,  gives  in  general  the  reactions  of  the  tree  to  the  different  degrees 
of  low  temperature  experienced: 

30  deg.  F. — Nothing  injured  so  far  as  could  be  observed. 

29  deg.  F. — No  injury  of  account;   only  traces  on  most  tender  growth  of 

West  Indian  and  Guatemalan  varieties. 
28  deg.  F. — New    foliage    scorched    on    Guatemalan    types;    West    Indian 

varieties   showing   considerable   foliage   damage. 
27  deg.  F. — Mexican  varieties  showed  new  tips  slightly  scorched;    Guate- 
malans showed  almost  all  new  foliage  injured;  West  Indians  badly 

damaged. 
25  to  26  deg.  F. — Mexican  varieties  showed  new  foliage  injured  but  some 

dormant  trees  uninjured;   all  Guatamalan  sorts  showed  new  foliage 

badly  injured  and  some  old  foliage  scorched. 
24  deg.  F. — Some     dormant     Mexican     varieties     uninjured;     Guatamalan 

varieties  badly  injured,  small  limbs  frozen  back. 
21  deg.  F. — All   Guatemalan  types  killed  to  bud;    a  few  of  the  hardiest 

Mexican  varieties,  such  as  Knowles  and  San  Sebastian,  with  young 

leaves   only   injured. 

Exceptions  occur  due  to  peculiar  local  conditions,  especially  as 
they  affect  individual  tree  vigor.  Varietal  differences  occur  within 
the  two  races  and  will  be  mentioned  later  (fig.  3). 

The  avocado  is  also  sensitive  to  hot  summer  temperatures.  This 
factor  is  the  main  reason  for  its  failure  in  the  hot,  dry,  interior 
sections.  Intense  heat  waves  in  the  more  favorable  districts  have 
caused  serious  damage  in  the  past.  Two  varieties,  the  Caliente  and 
the  Tiger,  have  shown  some  promise  of  heat  resistance  in  the  more 
arid  districts. 

Atmospheric  humidity  is  a  factor  of  importance  as  evidenced  by 
the  behavior  of  the  avocado  in  different  parts  of  the  state.  The  tree 
thrives  best  in  the  more  humid  coastal  districts.  Dry  atmospheric 
conditions  are  detrimental  as  evidenced  by  the  failure  of  trees  to 
succeed  in  the  Coachella  and  Imperial  valleys. 

Since  avocado  culture  is  carried  on  in  California  entirely  under 
irrigation,  the  question  of  rainfall  is  not  of  importance  except  as  it 
insures  an  adequate  supply  of  irrigation  water. 

Wind  has  an  important  influence  in  avocado  culture  and  is  dis- 
cussed in  another  section. 

On  account  of  the  wide  variation  in  climatic  conditions  within 
relatively  small  areas,  previously  alluded  to,  the  greatest  care  should 


1  Webber,  H.  J.     Cold  resistance  of  the  avocado.     California  Avocado  Associ- 
ation Annual  Keport  1917:   49.     1918. 


Bul.  365] 


AVOCADO   CULTURE  IN   CALIFORNIA 


13 


be  exercised  in  the  selection  of  a  site  for  the  avocado  orchard.  Not 
until  all  the  information  available  has  been  obtained  should  a  definite 
choice  be  made.  If  then  it  appears  that  the  climatic  conditions  are 
suitable,  choice  of  varieties  should  be  made  on  the  basis  of  both 
climatic  and  economic  considerations  (see  section  on  varieties). 


Fig.  3. — Belative  frost  resistance  of  seedling  avocado  trees  of  Guatemalan 
and  Mexican  origin.  They  were  located  in  an  exposed  section  of  the  San  Gabriel 
Valley  with  no  frost  protection.     Injury  caused  by  cold  wave  of  January,  1922. 


SOILS 

Observations  on  the  behavior  of  the  avocado  in  California  indicate 
that  it  thrives  on  a  wide  range  of  soils.  Commercial  plantings  are 
found  on  the  very  light,  sandy  soils  and  on  the  heavy  black  adobes 
and  on  the  many  different  types  between  these  two  extremes.  It  seems 
to  do  best,  however,  on  the  medium-textured  soils.  For  satisfactory 
results  a  depth  of  at  least  four  feet  is  recommended.  The  avocado  is 
extremely  sensitive  to  poor  drainage  and  will  not  endure  a  saturated 
soil  for  more  than  a  few  days. 

In  selecting  the  site  for  the  avocado  orchard  the  character  of  the 
subsoil  should  be  most  carefully  determined.  Structural  faults  such 
as  clay  layers,  limestone,  or  hardpan  close  to  the  surface,  are  especially 


14  UNIVERSITY  OF  CALIFORNIA EXPERIMENT  STATION 

unfavorable  on  account  of  the  intolerance  of  the  avocado  to  poor 
drainage.  For  this  reason  soils  with  these  subsurface  characteristics 
should  be  avoided. 

California  soils  are  notably  variable  in  texture,  structure,  depth 
and  other  characteristics.  While  the  soil  survey  reports  are  remark- 
ably accurate  and  consequently  exceedingly  helpful,  obviously  they 
cannot  picture  in  detail  the  local  soil  variability.  This  can  only  be 
determined  by  personal  examination,  by  means  of  a  soil  auger  or  tube. 
Time  spent  in  studying  the  soil  conditions  is  unquestionably  in  most 
cases  a  profitable  investment  for  the  intending  avocado  planter.  He 
will  also  usually  find  it  advisable  to  consult  the  Farm  Advisor  in  the 
county  in  which  the  land  is  situated. 


PROPAGATION 

Root  stocks. — Experience  in  handling  and  growing  budded  avocado 
trees  during  recent  years  has  indicated  the  need  for  more  information 
concerning  the  choice  and  selection  of  rootstocks.  In  the  early  years 
of  the  industry  any  kind  of  seed  procurable  was  used  to  raise  seed- 
lings— West  Indian,  Guatemalan,  or  Mexican — large,  small,  mature 
and  immature — with  the  result  that  many  nursery  trees  failed  to 
make  a  satisfactory  growth,  and  many  young  orchard  trees  failed 
after  planting.  The  West  Indian  seedlings  were  early  discarded 
because  of  their  tenderness  to  frost ;  and  because  of  the  more  plentiful 
supply  of  seed  of  the  Mexican  varieties  for  some  years  most  of  the 
trees  were  propagated  on  this  stock.  In  recent  years,  however,  the 
situation  has  changed  materially,  in  that  seed  of  the  Guatemalan 
varieties  has  been  available  in  much  larger  quantities  than  is  the  case 
with  varieties  of  the  Mexican  race.  This,  coupled  with  the  fact  that 
avocado  seed  cannot  be  brought  in  from  Mexico  on  account  of  the 
avocado  seed  weevil,  has  resulted  in  many  trees  being  propagated  on 
the  Guatemalan  stock.  While,  in  general,  these  trees  appear  to  be 
satisfactory,  the  greater  susceptibility  of  this  stock  to  frost  is  a  factor 
which  should  be  given  serious  consideration  in  connection  with  its  use. 
There  can  be  little  question  but  that  the  Mexican  stock  is  the  prefer- 
able one  to  use,  on  account  of  its  greater  resistance  to  frost. 

The  wide  variation  in  Mexican  seedlings,  which  has  become 
especially  evident  in  recent  years,  leads  to  the  conclusion  that  many 
of  the  seeds  represent  natural  hybrids  resulting  from  cross  pollination 
from  nearby  Guatemalan  trees.  It  is  possible,  however,  on  the  basis 
of  the  leaf  and  coloration  characters  exhibited  by  the  seedlings,  to 


BUL.  365]  AVOCADO  CULTURE  IN  CALIFORNIA  15 

separate  out  many,  if  not  most,  of  the  hybrid  seedlings ;  and  a  number 
of  the  nurserymen  now  follow  this  practice  regularly.  There  is 
evidence  indicating  that  seedling  variation  from  this  cause  would  be 
greatly  minimized  if  seed  were  taken  only  from  isolated  trees  or  solid 
plantings  of  Mexican  varieties  where  the  opportunities  for  natural 
hybridization  are  remote. 

On  account  of  its  remarkable  vigor,  large  numbers  of  trees  have 
been  propagated  in  recent  years  on  seedlings  of  the  Fuerte  variety, 
which  seem  to  be  fairly  uniform  and  vigorous.  Seed  is  generally 
obtained  from  dealers,  of  which  there  are  several  specializing  in 
avocado  seeds,  or  from  the  cooperative  marketing  agency.  The  seed 
should  be  from  fully  matured,  well-developed  and  well-shaped  fruit, 
rather  than  from  under-sized  and  immature  fruit. 

Growing  the  Seedlings. — Several  methods  are  used  in  starting  the 
seeds,  differing  only  in  minor  details.  The  seeds  are  usually  planted 
in  boxes  or  beds  containing  at  least  six  inches  of  a  mixture  of  loam 
and  clear  sand,  a  mixture  of  half  of  each  being  a  common  practice. 
The  seeds  are  planted  base  downward  with  the  apex  barely  protruding 
above  the  soil.  Large  beds  are  sometimes  made  either  over  a  hotbed 
or  in  the  open.  Muslin  or  lath  screens  are  placed  over  the  beds  during 
the  hottest  part  of  the  day  during  hot  weather.  It  was  formerly  a 
rather  common  method  to  plant  the  seeds  in  pots,  but  this  practice  has 
for  the  most  part  been  discontinued.  They  are  best  planted  as  soon  as 
possible  after  removal  from  the  fruit,  but  may  be  kept  several  months 
if  not  permitted  to  dry  out.  Since  most  of  the  Mexican  varieties 
ripen  in  late  summer  and  fall,  seed  is  usually  planted  during  this 
time  of  the  year.  Growth  starts  in  late  winter  or  early  spring,  so  that 
the  seedlings  are  ready  to  be  set  out  in  March  or  April  when  they 
have  attained  a  height  of  four  to  eight  inches. 

When  danger  of  frost  is  over  and  the  seedlings  have  reached  the 
height  mentioned,  they  are  usually  transplanted  directly  to  the  nursery 
rows,  fourteen  to  eighteen  inches  apart  in  the  row,  and  the  rows  forty 
inches  to  four  feet  apart.  It  is  considered  good  practice  to  clip  off 
about  two-thirds  of  each  expanded  leaf  at  the  time  of  transplanting. 
Irrigation  should  immediately  follow  planting  to  prevent  drying  out. 
If  the  weather  is  particularly  warm,  temporary  protection  from  the 
sun  is  necessary  and  is  usually  provided  by  placing  a  shingle  on  the 
south  side  of  each  seedling.  Some  nurserymen  have  in  the  past 
planted  the  seedlings  in  four-inch  pots,  later  setting  them  out  in  the 
field  from  the  pots  before  or  after  budding.  Because  of  danger  of  the 
curling  of  the  roots  at  the  bottom  of  the  pot,  which  may  result  in 
permanent  injury,  this  practice  has  been  discontinued.    It  can  be  used 


16  UNIVERSITY  OF  CALIFORNIA EXPERIMENT  STATION 

with  safety  where  the  seedlings  are  held  only  from  three  to  four  weeks 
before  transplanting.  Frequent  watering  is  necessary  until  they 
become  established,  after  which  irrigation  every  two  weeks  should 
be  sufficient  excepting  in  extremely  hot  weather. 

Budding. — The  operation  of  budding  is  simple,  but  must  be  carried 
out  with  unusual  care  and  attention  in  every  detail  to  insure  success. 
Most  of  the  failures  common  to  the  beginner  are  directly  traceable 
to  the  neglect  of  some  detail.  The  selection  of  bud-wood  must  be 
made  with  unusual  care  and  with  a  knowledge  of  the  peculiarities  of 
each  variety. 

Seedlings  to  be  used  for  budding  should  be  kept  in  a  thrifty, 
growing  condition.  They  may  be  budded  any  time  during  the  season 
when  the  sap  is  flowing  freely,  after  they  have  attained  a  diameter 
of  one-half  inch.  Uusually  this  occurs  early  in  the  spring,  April  and 
May  being  the  usual  months  for  the  operation.  For  budding  during 
these  months,  well  matured  wood  from  the  previous  season's  growth 
may  be  used.  After  active  growth  has  commenced,  suitable  buds  are 
not  available  until  the  new  growth  has  hardened,  usually  by  the  latter 
part  of  June.  At  this  time  budding  can  again  be  commenced  and 
continued  until  late  in  the  fall.  A  certain  percentage  of  the  buds 
inserted  in  the  fall  will  push  out  and  make  some  growth  and  will 
require  extra  protection  during  the  winter.  Only  buds  put  in  very 
late  in  the  fall  can  be  counted  on  to  remain  dormant  until  spring. 

Ordinarily  wood  that  is  well  matured  with  fairly  plump  buds, 
that  is,  not  hard  and  yet  does  not  snap  on  bending,  furnishes  the  best 
material  for  buds  (fig.  4).  The  Fuerte  will  give  high  percentage 
stands  from  young  buds  taken  almost  to  the  tip  of  young  growth. 
Intimate  knowledge  of  the  peculiarities  of  each  variety  comes  only 
with  practice  and  observation. 

Shield  budding,  such  as  is  used  in  the  propagation  of  citrus  and 
deciduous  fruits,  is  the  common  nursery  practice.  A  "T"  incision 
is  made  within  two  or  three  inches  of  the  ground,  preferably  on  the 
north  side  of  the  seedling.  The  bud  is  cut  with  a  shield  not  less  than 
an  inch  and  a  quarter  in  length,  and  is  pushed  gently  into  the  incision. 
The  stock  should  be  in  such  condition  of  growth  that  the  bark  will 
slip  readily,  and  will  not  require  lifting  by  the  knife  blade,  otherwise 
it  is  too  dry  to  be  used  successfully. 

The  knife  blade  used  for  cutting  buds  should  be  thin  and  should 
be  kept  at  a  razor  edge.  The  cut  should  be  made  parallel  to  the 
surface  of  the  stick  with  a  single,  sliding  motion ;  much  of  the  success 
of  budding  depends  on  having  the  cut  uniform,  smooth  and  straight. 


BuL.  365]  AVOCADO  CULTURE  IN   CALIFORNIA 


17 


Fig.  4. — Desirable  types  of  bud-wood  used  in  the  propagation  of  avocado  trees. 


18  UNIVERSITY  OF  CALIFORNIA EXPERIMENT  STATION 

After  insertion,  the  bud  is  immediately  wrapped,  beginning  at 
the  top  and  working  down.  Various  materials  are  used ;  raffia,  cotton 
twine,  rubber  bands,  muslin,  and  budding  cloth,  all  are  employed. 
Budding  cloth  is  recommended,  provided  a  hard  wax  is  used  in  its 
manufacture  which  will  not  melt  and  injure  the  bud  in  hot  weather. 
A  wax  composed  of  one  pound  of  beeswax  and  one  quarter  of  a  pound 
of  rosin  is  satisfactory.  Cheap  grades  of  muslin  are  made  up  into 
rolls  six  inches  wide  and  one  inch  in  diameter,  and  boiled  in  the  wax 
for  fifteen  minutes. 

About  three  weeks  are  required  for  the  buds  to  unite  with  the 
stock,  during  which  period  they  should  be  examined  and  the  wraps 
loosened  to  prevent  binding.  The  top  should  be  pinched  back  at  this 
time  in  order  to  start  the  bud  into  growth.  From  six  to  eight  weeks 
after  budding  the  wraps  may  be  safely  removed.  After  another  month 
of  growth  the  seedling  should  be  cut  back  still  further,  leaving  some 
foliage  to  take  care  of  the  sap  flow.  When  the  bud  has  made  a 
growth  of  four  to  six  inches  it  should  be  tied  up  to  the  stock  with 
raffia ;  staking  should  be  done  when  it  has  reached  a  height  of  sixteen 
to  eighteen  inches.  The  seedling  top  should  not  be  cut  off  until  the 
bud  has  grown  at  least  two  feet;  this  operation  is  best  done  when 
the  top  has  become  somewhat  hardened.  A  sloping,  smooth  cut  close 
to  the  bud  union  should  be  made  and  the  wound  painted  over  with 
grafting  wax. 

A  novel  adaptation  of  budding  has  been  developed  by  A.  R. 
Hideout,  of  Whittier,  in  an  effort  to  obtain  an  earlier  indication  of 
the  results  of  seed  selection.  Seeds  are  sprouted  in  the  regular  way. 
When  the  rootlets  are  about  an  inch  long,  one  of  the  two  halves  of  the 
seed  is  carefully  removed  without  disturbing  the  developing  plantlet. 
A  sharp  cut  is  made,  beginning  at  the  base  of  the  tiny  shoot  and 
extending  through  to  the  root  tip.  The  other  half  of  the  seed  is 
sometimes  cut  away,  leaving  a  small  wedge-shaped  portion  to  assist 
in  forcing  the  rootlet  into  the  incision,  or  it  may  be  left  on  entirely. 
The  sprouting  seeds  so  prepared  are  then  inserted  in  limbs  of  mature 
trees  or  on  nursery  stocks  by  means  of  long  "T"  incisions.  The  tip 
of  the  root  is  inserted  at  the  intersection  of  the  horizontal  and  vertical 
incisions  and  gently  forced  down  in  the  same  manner  as  in  shield 
budding,  until  the  split  radical  is  well  in  place.  Strips  of  specially 
prepared  budding  rubber  an  eighth  of  an  inch  in  width  are  used  to 
bind  the  sprouted  embryo  in  place  and  a  piece  of  dental  rubber 
sheeting  is  wrapped  over  the  area  to  prevent  drying  out  and  to 
exclude  the  entrance  of  water  from  without  until  union  has  taken 
place.    By  this  method  the  seedling  becomes  a  new  branch  on  a  mature 


Bul.  365] 


AVOCADO   CULTURE  IN   CALIFORNIA 


19 


tree  or  the  top  of  a  young  tree,  and  probably  will  come  into  fruiting 
considerably  sooner  than  if  grown  as  a  seedling  plant.  The  operation 
is  not  at  all  difficult  and  requires  only  care  on  the  part  of  the  operator. 


Fig.  5. — Year-old  budded  nursery  stock,  balled  ready  for  shipment. 


Balling. — It  is  the  customary  practice  to  ball  the  trees  prior  to 
the  starting  of  growth  in  the  spring,  and  to  hold  them  in  the  lath- 
house  until  planting  time,  although  some  nurserymen  prefer  to  delay 
balling  the  trees  until  ten  days  or  two  weeks  before  they  are  to  be 


20  UNIVERSITY  OF  CALIFORNIA EXPERIMENT  STATION 

planted  in  the  orchard.  A  few  days  before  balling",  the  trees  are  cut 
back  partially  or  partially  defoliated,  or  both,  to  balance  the  loss  of 
part  of  the  root  system.  The  cuts  should  be  waxed  to  prevent  excessive 
evaporation.  A  ball  of  earth  ten  to  twelve  inches  in  diameter  and 
fourteen  to  eighteen  inches  in  length  is  removed  with  each  tree 
(fig.  5).  The  trees  are  then  hardened  off  by  storing  under  lath  until 
planting  time.     Care  must  be  taken  to  keep  the  balls  moist. 

Some  experiments  have  been  tried  of  planting  budded  avocados 
with  bare  roots,  but  these  have  not  been  very  successful,  and  the 
practice  cannot  be  recommended. 

Nursery  Tree  Standards. — Until  recently  avocado  trees  were  sold 
by  height,  a  premium  being  paid  for  the  tall  trees.  It  became  apparent 
some  years  ago,  however,  that  the  tall,  slender  trees  frequently  did 
not  do  as  well  in  the  orchard  as  the  shorter  and  more  bushy  trees. 
They  often  failed  to  make  much  growth  for  several  years,  while  the 
smaller  trees  generally  started  off  immediately  and  within  a  year  or 
two  were  ahead  of  the  originally  larger  trees. 

This  experience  has  brought  about  a  rather  marked  change  in 
nursery  practice  in  the  past  two  years,  and  the  majority  of  the  trees 
are  now  sold  by  caliper,  the  measurement  being  taken  one  inch  above 
the  bud  union.  It  has  been  found  that  if  the  trees  are  not  forced  to 
grow  tall,  but  are  permitted  to  assume  a  bushy  habit,  they  are  more 
stocky  and  do  better  when  set  out  in  the  orchard.  Such  trees  do  not 
require  expensive  staking  and  protection  from  sunburn,  though  wind 
protection  is  necessary,  regardless  of  the  type  of  nursery  tree. 

At  least  one  of  the  larger  avocado  nurseries  now  sells  all  trees  on 
the  basis  of  two  grades,  guaranteeing  the  buds  to  be  from  bearing 
trees  of  good  yield  record,  and  the  stocks  to  be  of  pure  Mexican 
parentage.  The  relatively  high  cost  of  nursery  trees  and  of  bringing 
an  avocado  orchard  into  bearing  makes  it  especially  important  that 
only  the  best  possible  trees  be  used.  Buds  from  record  trees  in  fruit 
usually  sell  at  from  three  to  five  cents  each. 

Topworking. — The  occurrence  of  many  unproductive  trees  and 
trees  producing  inferior  types  of  fruit  has  created  much  interest  in 
methods  of  working  them  over  to  desirable  productive  strains.  Several 
successful  methods  have  been  developed;  of  these,  budding  and  cleft 
grafting  are  the  most  generally  used.  In  budding  over  large  trees, 
buds  are  inserted  directly  into  the  old  bark  on  the  trunk  or  main 
limbs  wherever  possible  in  order  to  save  time  and  to  form  the  new 
top  close  to  the  head.  Budding  can  be  done  only  when  the  sap  is 
flowing  freely  and  the  bark  raises  easily,  usually  from  April  to 
November. 


BUL.  365]  AVOCADO  CULTURE  IN  CALIFORNIA  21 

From  one-third  to  one-half  of  the  top  is  first  removed  by  a 
thinning-out  pruning.  The  trunk  and  limbs  exposed  should  be  given 
a  coat  of  whitewash  to  prevent  sunburn.  From  two  to  four  buds  are 
inserted  in  each  of  the  branches  to  be  budded  in  such  a  manner  that 
one  wrapping  suffices  for  all.  One  or  two  "safety"  limbs  are  generally 
left  to  nourish  the  roots  and  take  the  surplus  sap  until  the  new  head 
is  established,  after  which  they  are  removed. 

Buds  are  taken  from  mature  wood  one-half  to  one  inch  in  diameter. 
They  are  cut  to  a  length  of  about  two  inches,  the  upper  or  lower  end 
being  cut  off  square  to  facilitate  forcing  the  bud  into  the  incision, 
according  to  whether  the  ordinary  "T"  or  inverted  "T"  incision  is 
used.  Where  the  bark  is  very  thick  it  is  scraped  as  an  aid  to  easy 
insertion.  The  wrapping  commonly  used  is  No.  16  white  cotton  string; 
it  is  wound  tightly  over  the  bud,  leaving  only  the  eye  exposed.  This 
wrapping  should  be  left  on  for  at  least  two  months,  since  if  cut  earlier 
the  bark  on  large  trees  has  a  tendency  to  lift  away  from  the  bud. 
Sucker  growths  are  removed  in  order  to  start  the  buds  into  growth. 
The  new  buds  are  carefully  tied  to  the  limbs  to  prevent  breaking. 
The  budded  limb  should  not  be  cut  back  until  the  new  growth  has 
become  somewhat  hardened  and  is  able  to  take  care  of  the  sap  flow; 
this  operation  is  usually  done  the  following  season.  It  may  be 
necessary  to  pinch  back  the  bud-shoots  to  encourage  early  branching. 

Considerable  time  can  be  saved  if  cleft-grafting  is  used  instead 
of  budding.  The  drawback  to  this  method  is  the  increased  cost  of 
scions.  Fewer  can  be  taken  from  any  one  tree  because  of  the  excessive 
amount  of  cutting  back  required  to  secure  them.  Where  trees  have 
well-formed  heads  consisting  of  two  or  three  well-spaced  framework 
limbs,  a  new  head  can  be  built  by  inserting  two  scions  in  each,  event- 
ually removing  one  of  the  scions  if  both  take,  leaving  the  more 
vigorous.  Limbs  not  used  for  grafting  are  gradually  removed  as  the 
new  top  develops  and  is  able  to  take  care  of  the  entire  sap  flow.  Very 
large  trees  with  no  branches  close  to  the  ground  can  be  successfully 
reworked  by  cutting  off  the  trunk  at  a  height  of  about  four  feet  and 
inserting  at  least  four  scions.  Special  precautions  must  be  taken  to 
keep  large  wounds  well  protected  against  the  entrance  of  heart  rot 
fungi  by  the  use  of  waterproof  paint  or  wax. 

Avocado  wood  is  unusually  brittle  and  in  sawing  off  limbs  to  be 
grafted  the  first  cut  should  be  made  about  a  foot  or  more  above  the 
point  where  the  scions  are  to  be  inserted.  This  is  done  to  prevent 
splitting,  and  permits  the  second  cut  to  be  made  clean  and  smooth. 
The  scions  should  be  of  second  growth  wood,  well  matured,  and  should 
have  two  or  three  buds  well  placed,  plump  and  well  formed,  but  not 


22 


UNIVERSITY  OF  CALIFORNIA EXPERIMENT  STATION 


far  advanced.  It  is  especially  desirable  for  the  scion  to  include  a 
growth  made  near  the  base  so  that  advantage  may  be  taken  of  the 
many  adventitious  buds  arising  in  that  zone.  This  insures  growth, 
once  union  is  effected.  The  scions  are  cut  wedge-shaped,  tapering 
for  a  distance  of  one  and  a  half  to  two  inches,  depending  somewhat 
upon  the  size  of  the  wood  used  and  the  limbs  to  be  grafted.  The 
cuts  are  also  tapered  slightly  from  front  to  back,  giving  a  very  slight 


Fig.  6. — Avocado  tree  topworked  by  cleft  grafting.     Note  the  nurse  limbs 
left,  whitewashed  trunk  and  branches,  and  paper  bag  protectors. 

wedge  shape,  enabling  the  scion  to  fit  more  closely  into  the  cleft.  Much 
of  the  success  in  topworking  depends  upon  making  the  cuts  smooth 
and  even,  and  the  knife  used  for  this  purpose  should  be  kept  at  razor 
sharpness  by  means  of  frequent  stropping. 

The  cleft  is  made  with  an  ordinary  butcher's  cleaver,  care  being 
taken  to  split  the  limb  some  distance  beyond  that  required  by  the 
length  of  the  scions.  This  reduces  the  pressure  exerted  on  them.  The 
edges  of  the  cleft  should  be  trimmed  smooth  with  a  knife.  A  hard- 
wood wedge  is  driven  into  the  center  of  the  cleft  and  the  scions  fitted 


BUL.  365]  AVOCADO  CULTURE  IN  CALIFORNIA  23 

so  that  the  cambium  layer  of  the  scion  and  that  of  the  stock  coincide 
as  closely  as  possible  throughout  their  entire  length.  The  wedge  is 
then  removed  and  budding  cloth  strips  half  an  inch  in  width  are 
wrapped  tightly  around  the  end  of  the  limb.  Grafting  wax  is  painted 
over  the  surface  of  the  cuts  and  poured  down  into  the  cleft  so  as  to 
fill  it.  The  tops  of  the  scions  are  tipped  with  wax.  Where  the  bark 
is  thick,  necessitating  the  setting  in  of  the  scions,  the  space  between 
the  bark  and  the  scions  is  also  filled  with  wax  before  the  budding 


Fig.  7. — Bark  grafted  avocado  limb.     The  cut  surface  should  be  well 
protected  by  a  waterproof  coating. 

cloth  wrapping  is  applied.  The  operation  is  completed  by  placing  a 
paper  bag  over  the  end  of  the  limb,  cutting  a  small  hole  for  ventilation. 
This  is  not  removed  until  the  scions  have  made  a  good  start.  The 
trunk  and  branches  should  be  protected  against  sunburn,  preferably 
by  whitewashing  (fig.  6). 

Various  sorts  of  grafting  waxes  and  wound  compounds  are 
employed,  one  of  the  most  common  being  a  mixture  of  three  parts 
of  rosin  and  one  of  beeswax.  In  recent  years  a  commercial  prepar- 
ation, which  appears  to  be  a  water-asphaltum  emulsion,  has  come  into 
prominence  and  is  now  extensively  used. 

Recently  a  modification  of  the  cleft-grafting  method  has  been 
developed,  which  appears  to  be  phenomenally  successful.  Instead  of 
splitting  the  stubs  after  cutting  off  the  branches,  they  are  deeply 


24  UNIVERSITY  OF  CALIFORNIA EXPERIMENT  STATION 

notched  with  a  saw.  Large  scion  wood  is  used,  the  scions  usually  being 
cut  rather  short,  with  one  or  two  buds.  These  are  cut  so  as  to  exactly 
fit  the  notches  and  are  driven  tightly  in  place.  Then  all  cut  surfaces 
are  waxed  and  the  sacks  attached,  the  trunk  and  branches  white- 
washed. 

Cleft  and  notch  grafting  are  successful  only  when  the  sap  flow  is 
slow  and  the  bark  does  not  slip.  These  methods  are  used  most  in 
January  and  February,  though  they  are  sometimes  successful  as  late 
as  March  and  April. 


Fig.  8.— Side  grafting  of  the  avocado.     This  method  can  be 
used  any  time  when  the  bark  slips  readily. 

The  follow-up  work  is  of  especial  importance.  Rewaxing  is  usually 
necessary  to  prevent  drying  out.  Supports  should  be  provided  early 
to  hold  up  the  rapidly  growing  shoots.  These  are  best  supplied  by 
tying  two-inch  pieces  to  the  limbs  on  which  the  scions  .are  located; 
this  allows  flexibility  and  at  the  same  time  sufficient  rigidity  to  insure 
adequate  support.  These  supports  will  need  to  be  lengthened  from 
time  to  time,  even  after  the  growth  is  six  to  eight  feet  high,  until  it 
is  well  hardened. 

Cleft  grafting  methods  have  the  advantage  that  in  the  event  of 
failure  of  the  scions  the  new  shoots  arising  from  the  cut  ends  of  the 
branches  can  be  thinned  and  budded  in  the  same  manner  as  nursery 


BUL.  365]  AVOCADO  CULTURE  IN  CALIFORNIA  25 

seedlings.  They  are  usually  large  enough  for  budding  by  June  or 
July.  Bracing  the  young  budded  shoots  is  especially  important  the 
first  season  or  two  as  they  are  very  easily  broken  off. 

Other  methods  of  topworking  which  have  been  used  with  success 
are  bark  grafting  and  side  grafting.  In  the  former  the  limb  or  trunk 
is  cut  off  square,  and  the  incisions  are  made  from  this  point  down- 
ward for  a  distance  of  about  two  inches  (fig.  7)  ;  in  the  latter  the 
regular  vertical  ' '  T "  incision  used  in  budding  is  made  on  the  side  of 
the  limb  or  trunk  (fig.  8).  Cutting  back  is  done  after  the  scions  have 
developed.  The  scions  are  selected  from  well  matured  wood  and  made 
with  a  long  sloping  cut  on  one  side  only.  They  are  pushed  down 
into  the  incision  after  the  manner  of  budding.  Tying,  waxing  and 
follow-up  work  are  the  same  as  for  the  other  methods.  These  two 
types  of  grafting  are  best  done  in  the  active  growing  season  during  the 
summer  months,  as  success  depends  on  the  easy  lifting  of  the  bark. 

Seedlings  and  named  varieties  exhibit  a  wide  variation  in  the  ease 
with  which  they  may  be  worked  over  to  some  other  desired  variety. 
The  Taft  seems  particularly  difficult  to  topwork  by  cleft  grafting; 
some  others  behave  in  a  similar  manner.  The  congeniality  between 
the  tree  to  be  topworked  and  the  desired  variety  from  which  scions 
will  be  taken  should  be  learned  if  possible  before  attempting  the 
operation. 

ORCHARD   MANAGEMENT 

Laying  Out  the  Orchard. — Two  general  systems  of  planting  are 
in  use :  the  square  system,  adapted  to  the  gently  sloping  and  more 
level  lands,  and  the  system  of  terrace  planting  used  on  the  steeper 
hill  slopes.  In  the  ordinary  square  system  planting  distances  vary 
from  15  x  15  feet  to  30  x  30  feet,  according  to  variety.  Some  of  the 
tall,  upright-growing  varieties  are  being  set  at  the  minimum  distance 
given,  while  the  Fuerte  and  similar  strong  growing  varieties  are  being 
planted  from  24  to  30  feet  apart,  with  a  preference  for  the  latter 
distance.  With  certain  varieties,  under  favorable  conditions  of  soil 
and  climate,  this  distance  may  have  to  be  increased  as  more  is  learned 
about  the  growth  of  the  budded  avocado  tree. 

In  recent  years  the  development  of  hillside  lands  for  avocado 
plantings  has  come  into  considerable  prominence.  On  account  of  the 
protection  from  frost  afforded  by  the  elevation,  extensive  hillside 
plantings  have  been  made,  especially  in  the  North  Whittier  Heights, 
La  Habra  and  Whittier  districts  (fig.  9).  This  system  is  of  course 
more  expensive  because  of  the  greatly  increased  cost  of  laying  out 


26  UNIVERSITY  OF  CALIFORNIA EXPERIMENT  STATION 

the  orchard  and  the  higher  costs  of  orchard  management.  The  limit 
of  the  steepness  of  the  slope  beyond  which  it  is  not  practicable  to 
terrace  is  estimated  to  be  about  30  degrees.  The  contour  grade  varies 
from  1  to  2y2  per  cent,  according  to  the  distance  the  irrigation  water 
will  have  to  flow.  The  width  of  the  terraces  varies  from  seven  to 
sixteen  feet,  the  latter  distance  being  considered  the  better  when  the 
slope  permits.  With  narrow  terraces  nearly  all  cultivation  must  be 
done  by  hand.  The  trees  are  planted  two  to  five  feet  inside  the  edge  of 
the  terrace,  the  tendency  at  the  present  time  being  to  plant  them  in 
far  enough  so  that  irrigation  furrows  may  be  run  on  both  sides.     The 


Fig.  9. — Construction  of  terraces  for  an  avocado  orchard  near  La  Habra, 
California.     (Photo  by  Webber.) 

cost  of  terracing  hillside  land  varies  from  $100  to  $150  per  acre, 
according  to  the  steepness  of  the  slope  and  the  character  of  the  soil. 
Where  possible,  grading  should  be  done  so  that  winter  rains  can  have 
the  opportunity  of  settling  the  terraces  and  indicating  any  irregu- 
larities that  may  interfere  with  the  flow  of  irrigation  water.  It  is 
advisable  to  run  water  down  each  terrace  as  a  final  test  before  putting 
in  the  trees ;  changes  in  the  terraces  are  difficult  to  make  after  planting 
has  been  done.  The  distance  terraces  are  placed  apart  averages  about 
thirty  feet,  varying  according  to  the  slope  and  contour  of  the  hillside. 
They  may  be  brought  closer  together  or  spread  wider  apart,  necessi- 
tating the  elimination  of  some  of  the  planting,  or  the  addition  of  short 
rows  in  between  to  insure  filling  the  entire  space.  Special  care  is 
necessary  during  the  rainy  season  to  prevent  excessive  erosion.  Ade- 
quate surface  drainage  must  be  provided.     The  control  of  weeds  is 


Bul.  365] 


AVOCADO  CULTURE  IN   CALIFORNIA 


27 


more  difficult  on  terraced  plantings,  because  of  the  banks  between 
terraces  which  can  not  be  handled  by  horse  or  tractor  drawn  imple- 
ments. Trees  are  planted  15  to  40  feet  apart  on  the  terraces,  according 
to  variety. 

On  both  terraced  and  level  plantings  considerable  attention  has 
been  devoted  to  the  interplanting  of  different  varieties  with  the  idea 
of  removing  some  of  the  trees  when  they  reach  maturity.  For  this 
purpose  varieties  for  interplanting  should  have  either  an  upright, 


Fig.  10. — The  furrow  system  of  irrigation  is  commonly  used  on  terraces. 
The  length  of  the  furrows  should  not  exceed  three  hundred  feet. 


slender  habit  of  growth  or  early  bearing  qualities.     Double-planting 
has  much  to  commend  it  and  will  doubtless  increase. 

The  practice  of  replacing  diseased  or  decadent  citrus  trees  by 
avocados  is  on  the  increase  and  bids  fair  to  become  an  important 
method  of  establishing  avocado  orchards,  especially  in  the  old  citrus 
districts.  By  this  means  some  income  from  the  citrus  orchard  is 
received  while  the  avocado  trees  are  coming  into  bearing.  The  leveling 
and  irrigation  system  are  provided  for,  and  the  citrus  trees  offer  con- 
siderable protection  to  the  young  avocado  trees.  Thus  far  the  avocado 
seems  to  be  practically  immune  to  the  attacks  of  gophers.  The  method 
is  being  watched  with  interest. 


28  UNIVERSITY  OF  CALIFORNIA EXPERIMENT  STATION 

There  is  at  least  one  possible  drawback  to  this  practice.  The  polli- 
nation of  those  varieties,  the  blooming  period  of  which  coincides  with 
that  of  citrus  trees,  would  possibly  suffer  from  the  fact  that  bees  seem 
to  prefer  citrus  flowers.  Placing  additional  hives  in  the  orchard  may 
overcome  the  difficulty.    Definite  information  on  this  point  is  lacking. 

Planting  and  Care  of  Young  Trees. — It  has  been  the  experience  in 
California  that  young  avocado  trees  are  much  more  tender  than  citrus 
trees,  and  hence  require  more  care  and  attention,  at  least  during  the 
first  few  years.  The  usual  methods  of  planting  and  caring  for  citrus 
trees  have  frequently  resulted  in  serious  losses  in  young  avocado 
orchards.  On  the  other  hand,  if  properly  planted  and  attended  to, 
avocado  trees  grow  rapidly  and  within  a  few  years  outdistance  citrus 
trees  of  the  same  age. 

It  is  almost  the  universal  practice  to  ball  avocado  trees  in  the 
nursery,  even  though  they  may  be  grown  for  planting  only  a  short 
distance  away.  This  practice  is  unquestionably  to  be  recommended, 
as  the  young  nursery-grown  trees  are  exceedingly  tender  and  very 
easily  injured  by  exposure  or  careless  handling.  Especial  care  must 
be  exercised  in  handling  the  trees  after  they  have  been  balled.  They 
should  never  be  picked  up  by  the  trunk  or  dropped  to  the  ground 
even  though  the  distance  be  short.  The  tearing  away  of  the  tender, 
fibrous  roots  and  the  breaking  of  the  contact  between  roots  and  soil 
incident  to  such  treatment  are  almost  certain  to  delay  the  starting  of 
growth  until  several  months  after  planting,  during  which  period  sun- 
burn is  quite  likely  to  occur. 

In  deep,  fertile  soils  the  digging  of  large  holes  is  unnecessary,  but 
in  many  soils  experience  has  shown  the  advisability  of  digging  large 
holes  and  filling  in  with  top  soil.  On  account  of  the  extreme  sensitive- 
ness of  the  bark  to  sunburn  the  bud-unions  should  be  faced  toward  the 
afternoon  sun.  The  soil  should  be  thoroughly  firmed  about  the  ball 
before  irrigation,  rather  than  settling  the  soil  by  running  water  in 
the  partially  filled  holes.  Placing  manure  or  other  fertilizers  in  the 
holes  is  not  recommended  as  it  is  likely  to  result  in  injury  to  the 
young,  tender  roots.  Pulling  back  the  corners  of  the  burlap  coverings 
of  the  balls  and  covering  them  with  soil  at  the  time  of  planting  is 
advisable  as  this  permits  better  contact  between  the  soil  in  the  ball 
and  that  in  which  the  trees  are  planted.  The  young  trees  should  never 
lack  for  moisture ;  they  should  be  irrigated  immediately  after  planting 
and  at  frequent  intervals  thereafter  until  well  established.  The 
interval  may  then  be  lengthened  to  two  or  three  weeks  in  accordance 
with  soil  and  climatic  conditions. 


BuL.  365]  AVOCADO  CULTURE  IN  CALIFORNIA  29 

Protection  against  sunburn  was  of  especial  importance  for  the 
slender,  upright  nursery  trees  formerly  used,  as  was  also  staking  to 
prevent  wind  damage.  With  the  more  compact  trees  of  the  type  now 
most  commonly  used  these  precautions  are  not  necessary,  though  some 
type  of  wind  shelter  or  screen  is  advisable  in  all  regions  of  either 
occasional  or  prevailing  winds. 

Cultivation  to  prevent  the  soil  becoming  packed  around  the  young 
trees,  and  to  keep  down  weeds,  is  essential.  The  surface  soil  should  be 
maintained  in  optimum  condition  to  take  water  readily.  Some  growers 
have  found  it  a  good  practice  to  make  basins  and  mulch  the  surface 
around  young  trees  with  bean  straw  or  alfalfa  straw.  This  practice 
appears  to  be  especially  effective  where  the  soil  in  the  balls  is  heavier 
in  texture  than  the  soil  in  which  the  young  tree  is  set. 

Care  of  Mature  Orchards. — Cultural  operations  in  mature  avocado 
orchards  differ  little  if  any  from  those  practiced  in  citrus  orchards. 
Spring  plowing  or  disking  and  summer  cultivation  are  usually 
practiced.  Cultural  operations  should  be  designed  primarily  to  main- 
tain conditions  favorable  to  the  penetration  of  irrigation  water. 
Weeds  should  be  kept  down.  On  terraced  plantings,  plowing  one  way 
in  the  spring  is  about  all  that  can  be  done,  and  on  narrow  terraces  is 
accomplished  with  difficulty,  if  at  all.  As  the  trees  spread  out  and 
cover  such  terraces  the  point  is  reached  when  hand  work  alone  must 
be  relied  on. 

Since  the  avocado  is  by  nature  a  shallow  rooted  tree,  deep  culti- 
vation or  abrupt  changes  in  depth  of  plowing  or  cultivating,  are  likely 
to  cause  injury,  which  is  often  exhibited  in  an  excessive  shedding  of 
the  young  fruits. 

Irrigation. — In  general  the  water  requirement  of  avocado  trees  is 
similar  to  that  of  citrus  trees.     Both  are  native  to  regions  of  high 
rainfall  which  comes  during  the  growing  season.    The  root  system  os 
the  avocado  is  also  similar  to  that  of  the  citrus  trees,  the  feeding 
rootlets  being  fibrous  and  located  for  the  most  part  in  the  upper  fc 
feet  of  soil.    Hence  irrigation  practice  with  these  fruits  is  similar  in 
all    important    respects.     Both    require    the    presence    of    available 
moisture  in  the  soil  at  all  seasons  of  the  year,  and  yet  it  is  certain 
that,  under  many  conditions  at  least,  citrus  and  avocado  trees  ha 
been  severely  injured  by  excessive  irrigation  even  where  soil  drainau 
is  good.     This  seems  to  have  been  brought  about  by  attempts  on  the 
part  of  many  growers  to  maintain  the  soil  moisture  at  a  relati 
uniform  point. 

There  is  much  reason  for  believing  that  citrus  and  avocado  roots 
are  most  active  when  the  soil  moisture  is  at  a  point  considerably 


30  UNIVERSITY  OF  CALIFORNIA EXPERIMENT  STATION 

lower  than  the  normal  field  capacity  of  the  soils  in  which  they  are 
located.  If  this  be  true  it  is  necessary  then  for  the  soil  moisture  to 
fluctuate  from  its  normal  moisture  holding  capacity  to  some  point 
approaching  the  wilting  coefficient.  That  permitting  the  soil  to  dry 
out  appreciably  between  irrigations  is  definitely  beneficial  to  the 
growth  and  fruitfulness  of  both  avocado  and  citrus  trees  has  been 
amply  demonstrated  in  recent  years ;  and  that  this  practice,  unless 
carried  so  far  as  to  cause  pronounced  wilting,  cannot  result  in  injury 
from  lack  of  moisture  has  been  adequately  established  from  experi- 
ments conducted  in  the  California  Agricultural  Experiment  Station2 
and  elsewhere.  Experiments  have  shown  that  the  use  of  water  by 
plants  is  independent  of  the  amount  in  the  soil  so  long  as  the  moisture 
content  is  above  the  wilting  point. 

The  amounts  of  water  required  by  avocado  trees  vary  greatly  in 
different  parts  of  the  state,  and  depend  mainly  on  the  age  of  the  trees 
and  climatic  conditions.  In  the  hot  interior  regions  good  bearing  trees 
require  the  equivalent  of  thirty-five  to  forty  inches  of  rainfall,  while 
in  the  coastal  areas  twenty-five  to  thirty  inches  appears  to  be  sufficient. 
Since  the  rainfall  in  the  avocado  districts  is  in  general  less  than  the 
total  requirement  of  the  trees,  and  in  addition  comes  altogether  during 
the  winter  months,  irrigation  is  required  to  make  up  the  deficiency  and 
to  supply  the  needs  of  the  trees  during  the  dry  growing  season.  This 
is  usually  accomplished  by  applying  three  or  four  acre  inches3  of 
water  at  each  irrigation.  The  interval  of  application  should  be  deter- 
mined by  examination  of  the  soil.  The  only  satisfactory  way  to 
determine  moisture  conditions  is  to  examine  the  soil  to  a  depth  of  at 
least  four  feet.  This  can  be  done  to  best  advantage  in  most  soils  with 
a  soil  auger,  or  post  hole  auger.  This  should  be  a  regular  orchard 
practice. 

Methods  of  applying  irrigation  water  to  avocado  orchards  vary. 
The  prevalent  practice  is  the  use  of  furrows;  this  method  gives  satis- 
faction where  the  slope  is  not  too  steep  and  the  soil  not  so  porous  as 
to  result  in  loss  of  moisture  and  plant  food  by  excessive  penetration. 
For  terrace  plantings  (fig.  10),  furrows  should  not  exceed  three 
hundred  feet  in  length  for  ordinary  conditions;  furrows  anywhere 
from  three  hundred  to  four  hundred  feet  in  length  are  most  satis- 
factory. The  use  of  cross  furrows  to  supply  water  in  the  dry  portions 
of  the  tree  rows  is  recommended. 


2  Veihmeyer,    F.    J.      Some    factors    affecting   the   irrigation   requirements    of 
deciduous  orchards.     California  Agr.  Exp.  Sta.     Hilgardia  2  (6)  :  125-291.     1927. 

3  An  acre  inch  is  approximately  equivalent  to  the  flow  of  1  miner 's  inch  of 
water  in  50  hours  or,  conversely,  50  miner's  inches  flowing  for  1  hour  on  1  acre. 


Bul.  365 


AVOCADO   CULTURE  IN   CALIFORNIA 


31 


The  mulched-basin  system  has  been  tried  with  varying  success. 
Poorly  drained  basins  in  heavy  soils  have  been  known  to  cause  the 
death  of  trees  from  suffocation  during  the  rainy  season.  Opinions 
differ  in  regard  to  the  ultimate  success  of  the  mulched-basin  system. 
Some  growers  have  already  discontinued  its  use,  while  others  continue 


Fig.  11. — Special  equipment  has  been  developed  for  irrigating  hillside  plant- 
ings. The  distributor  shown  above  is  used  where  the  pipeline  passes  down  a. 
ridge  with  the  furrows  sloping  each  way  from  it.  It  is  jointed  so  that  it  can  be 
raised  vertically  to  be  out  of  the  way  of  cultural  operations. 

it  in  new  plantings.  It  reduces  the  amount  of  cultivation,  is  conducive 
to  the  maintenance  of  favorable  soil  moisture  and  temperature  con- 
ditions, and  supplies  organic  matter  to  the  soil — where  sufficient 
mulching  material  is  kept  in  the  basins.  However,  the  basins  are 
rather  costly  to  install  on  very  steep  slopes  and  are  expensive  to 
maintain. 


32 


UNIVERSITY  OF  CALIFORNIA EXPERIMENT  STATION 


On  the  lighter  soils  flooding  is  necessary  to  get  the  water  evenly 
distributed  over  the  entire  area,  since  a  sufficient  head  can  not  be 
maintained  to  carry  the  water  down  furrows. 


t'jef 


Fig.  12. — The  use  of  overhead  systems  of  irrigation  is  increasing.     The  above 
illustrates  one  of  several  types.     (From  Agr.  Ext.  Cir.  4). 


BUL.  365]  AVOCADO  CULTURE  IN   CALIFORNIA  33 

Much  attention  is  being  devoted  to  overhead  sprinkling  systems 
in  avocado  plantings,  following  the  example  of  some  of  the  citrus 
growers.  This  method  appears  to  be  decidedly  promising  (fig.  12). 
By  means  of  this  system  the  water  is  applied  uniformly,  furrowing  out 
is  not  required,  and  once  the  water  is  turned  on  but  little  attention  is 
needed.  A  modified  sprinkler  system  has  been  tried  under  the  trees, 
but  is  not  so  successful  because  the  limbs  usually  have  to  be  cut  high 
to  allow  the  spray  to  spread.  This  leaves  the  trunks  less  protected 
during  cold  weather  and  serious  damage  from  freezing  has  resulted. 
The  cost  of  installing  the  overhead  system  varies  from  $100  to  $350 
an  acre,  according  to  the  type  of  equipment  used. 

The  drip  system  has  been  used  by  some  growers,  but  does  not  give 
an  even  distribution  of  moisture  and  cannot  be  depended  upon  to  meet 
the  requirements  of  the  tree  during  the  growing  season. 

As  already  mentioned,  the  question  of  drainage  is  of  equal  import- 
ance with  irrigation.  The  avocado  tree  requires  an  abundance  of 
water,  but  it  must  also  have  thorough  drainage — both  surface  and 
subsoil.     The  tree  is  intolerant  to  standing  water. 

Fertilization. — Little  is  known  concerning  the  fertilization  of 
avocado  orchards.  Experience  in  both  Florida  and  California  has 
demonstrated  a  marked  response  to  applications  of  nitrogenous  fer- 
tilizers but  so  far  as  can  be  determined  no  carefully  planned  fertilizer 
experiments  have  ever  been  conducted  on  the. avocado.  The  results  of 
citrus  fertilization  studies  afford  the  best  information  available  at  the 
present  time  and  it  is  believed  they  are  applicable  to  the  avocado,  at 
least  to  a  considerable  degree.  Studies  of  the  soils  in  the  citrus 
districts  of  southern  California  have  disclosed  that  they  are  for  the 
most  part  relatively  well  supplied  with  potassium  and  phosphorus, 
two  of  the  three  elements  most  likely  to  be  deficient.  These  two 
require  only  the  presence  of  decaying  organic  matter  to  make  them 
available.  These  soils  are,  however,  prevailingly  deficient  in  nitrogen 
and  organic  matter  and  these  materials  are  applied  to  mature  citrus 
orchards  in  large  quantities  as  a  demonstrated  means  of  maintaining 
production. 

The  amounts  of  plant  food  elements  removed  from  the  soil  by 
avocado  trees  are  probably  as  large  as  those  removed  by  citrus  trees. 
The  avocado  fruit  is  high  in  mineral  content  and  in  protein,  and  it 
is  not  improbable  that  avocados  remove  more  elements  from  the  soil 
than  a  corresponding  crop  of  citrus  fruits.  The  entire  question  must 
be  given  thorough  scientific  investigation  before  any  definite  statements 
can  be  made.  For  mature  bearing  trees  the  use  of  two  pounds  of 
nitrogen  per  tree  per  year  is  a  safe  minimum ;  at  least  half  of  it  should 


34  UNIVERSITY  OF  CALIFORNIA EXPERIMENT  STATION 

be  secured  from  organic  sources,  preferably  bulky  manures.  No 
better  general  fertilizer  can  be  recommended  than  good  barnyard 
manure.  Alfalfa  hay  and  beanstraw  are  likewise  very  satisfactory 
materials  when  they  can  be  secured  at  a  reasonable  price.  These  bulky 
materials  are  best  turned  under  during  the  fall  of  the  year.  With 
citrus  trees  the  use  of  a  quickly  available  nitrogenous  fertilizer,  such 
as  nitrate  of  lime,  has  proved  of  value  in  helping  to  set  the  crop  when 
applied  from  four  to  six  weeks  in  advance  of  the  blossoming  period. 
There  is  reason  to  believe  that  a  similar  practice  is  beneficial  to  the 
avocado. 

The  fertilization  of  young  avocado  trees  offers  a  different  problem 
from  that  of  older  trees.  The  excessive  use  of  nitrogenous  fertilizers 
seems  to  have  caused  many  to  delay  coming  into  bearing.  The  incor- 
poration of  quantities  of  barnyard  manure  in  the  pits  in  which  young 
trees  are  to  be  planted  is  not  to  be  recommended  except  to  a  limited 
degree  in  very  heavy,  tight  soils.  In  these  cases  the  manure  should  be 
placed  at  the  very  bottom  of  the  pit  and  mixed  thoroughly  with  the 
soil.  Young  trees  will  make  a  better  growth  if  top  soil  is  used  to  fill 
in  the  holes  and  if  the  use  of  fertilizers  is  withheld  until  the  trees 
have  come  into  bearing.  Exceptions  are  to  be  made,  of  course,  in  the 
case  of  very  poor  soils. 

Cover  crops  have  long  been  used  successfully  as  a  means  of  par- 
tially supplying  the  organic  matter  requirements  of  citrus  trees,  and 
are  being  used  to  some  extent  in  avocado  orchards.  Winter  cover 
crops — usually  purple  vetch  (View,  atropurpurea)  or  bitter  clover 
(Melilotus  indica)  are  generally  used  because  of  winter  rainfall. 
Where  irrigation  water  is  plentiful  and  cheap  during  the  summer 
months,  sweet  clover  (Melilotus  alba)  may  be  grown  to  advantage. 
It  is  of  particular  value  on  heavy,  tight  soils,  because  of  the  action  of 
its  large,  deep-growing  roots  in  opening  up  the  subsoil  and  supplying 
organic  matter  and  better  moisture  penetration  to  the  lower  layers. 

Pruning. — No  systematic  study  has  been  made  concerning  the 
pruning  of  the  avocado.  However,  observations  which  have  been 
made  over  a  period  of  some  years  relative  to  different  practices  used 
by  growers,  together  with  principles  applicable  to  other  evergreen 
fruit  trees,  point  to  some  fairly  clear  generalizations.  The  avocado 
requires  little  or  no  pruning  once  its  framework  has  been  established. 
Some  thinning  from  time  to  time  will  be  advisable  to  permit  sunlight 
to  reach  the  inside  foliage.  In  some  strong  growing  varieties  cross 
branches  develop  which,  if  allowed  to  remain,  result  in  poorly  formed 
tops  and  severe  breakage.  Stubbing  back  should  be  avoided,  as  the 
resulting   crop   of  vigorous   sprouts   only   complicates   the   problem. 


BUL.  365]  AVOCADO  CULTURE  IN  CALIFORNIA  35 

Mechanically  weak  growth  should  also  be  removed  early,  in  order  to 
eliminate  causes  of  breakage. 

Little  or  no  heading  back  should  be  given  young  trees.  In  cases 
where  a  head  is  not  naturally  formed  low  enough,  cutting  back  may 
be  necessary.  Examination  of  the  trunk  of  a  young  tree  will  reveal 
several  cycles  of  growth,  each  terminated  by  a  series  of  dormant  buds. 
The  cut  should  be  made  just  above  the  strongest  of  these  buds,  which 
on  starting  usually  make  an  upright  growth.  The  practice  of  heading 
back  to  laterals  with  the  hope  of  developing  one  of  these  into  a  head 
has  not  been  successful.  In  some  of  the  weaker  growing  types,  short- 
ening in  to  strong  buds  has  been  reported  successful  in  strengthening 
the  stock  and  framework  of  the  trees  while  young.  Heavy  pruning 
of  young  trees  greatly  accentuates  vegetative  growth  and  delays  the 
fruiting  period.  Observations  by  Bioletti  indicate  that  better  tree 
growth  is  obtained  in  young  evergreen  fruit  trees  where  little  or  no 
pruning  is  given,  as  compared  with  trees  more  heavily  pruned. 

HARVESTING 

With  the  varieties  now  grown  in  California,  avocado  fruits  ripen 
every  month  in  the  year.  Since  the  fruit  will  not  soften  on  the  tree 
and  the  external  indications  of  maturity  are  often  almost  impercept- 
ible, considerable  difficulty  is  frequently  experienced  in  determining 
the  proper  period  for  harvesting.  With  most  of  the  dark  colored 
varieties  this  is  usually  not  especially  difficult,  for  by  the  time  the 
skin  is  fairly  well  colored  the  fruits  are  ordinarily  in  proper  condition 
for  picking.  There  are  exceptions,  however,  even  in  the  dark  colored 
sorts.  The  difficulties  are  much  greater  with  the  green  varieties, 
though  it  is  usually  possible  for  the  experienced  grower  to  detect 
slight  changes  in  the  color  of  the  skin  and  stem  as  they  approach 
maturity.  The  brightness  of  the  skin  color  usually  diminishes  and 
a  slight  yellowish  tint  to  both  skin  and  stem  often  develops;  there  is, 
however,  no  safe  and  certain  criterion  of  horticultural  maturity  except 
the  laboratory  determination  for  oil  content. 

The  ripening  seasons  of  the  different  varieties  vary  notably  from 
season  to  season,  and  also  differ  widely  in  the  different  sections.  The 
variation  from  season  to  season  relates  somewhat  to  weather  conditions 
but  is  apparently  affected  even  more  by  the  setting  period  of  the 
bloom,  which  is  often  distributed  over  three  or  four  months.  Variation 
in  maturity  in  the  different  sections  appears  to  be  related  to  differences 
in  the  amounts  of  heat  during  the  year.  In  general,  the  hotter, 
interior  districts  are  the  earliest  to   ripen  the  fruit  and  the   cool 


36  UNIVERSITY  OF  CALIFORNIA EXPERIMENT  STATION 

coastal  areas,  the  latest,  though  differences  in  the  period  of  setting 
sometimes  more  than  offset  the  normal  differences  in  season  of  maturity 
in  the  different  regions. 

In  order  to  provide  for  uniformity  in  the  maturity  of  the  fruit  at 
the  time  of  harvesting  and  especially  to  prevent  the  sale  of  immature 
avocados,  which  practice  had  become  a  menace  to  the  industry,  the 
California  avocado  growers  in  1925  succeeded  in  having  a  state 
maturity  standard  of  eight  per  cent  fat  or  oil  content  established. 
This  action  has  been  productive  of  very  great  benefit  to  the  industry 
in  that  it  has  rather  effectively  eliminated  immature  fruit,  mostly 
windfalls  or  stolen  fruit,  from  the  markets.  It  is  quite  generally  felt 
that  the  standard  is  still  too  low  for  the.  Mexican  and  Guatemalan 
varities,  as  is  evident  from  the  fact  that  the  requirements  for  the 
best  grades  of  fruit  marketed  by  the  Calavo  Growers  of  California  are 
considerably  higher.  As  further  information  is  developed  concerning 
the  normal  range  of  fat  content  of  the  different  varieties  it  may 
become  desirable  to  raise  the  standard  somewhat.  The  refractometer 
method  of  oil  determination  has  been  found  to  be  relatively  accurate, 
and  this  method  is  now  used  almost  exclusively. 

The  fruits  are  clipped  from  the  trees  in  the  same  manner  as 
lemons,  double  cutting  being  employed  to  insure  that  the  stem  is  cut 
flush  with  the  base  of  the  fruit.  They  should  never  be  pulled  from  the 
trees  as  the  removal  of  the  pedicel  or  "button"  with  most  varieties 
is  almost  certain  to  result  in  decay.  On  account  of  the  greater  tender- 
ness of  the  fruit  it  must  be  handled  most  carefully.  The  use  of  small 
canvas  picking  bags  or  buckets  is  advised  as  a  means  of  preventing 
bruising  of  the  fruit. 

FROST   INJURY   AND    FROST   PROTECTION 

Owing  to  the  newness  of  the  industry,  comparatively  little  is  known 
relative  to  the  treatment  of  frost  injured  trees.  Varieties  differ  widely 
in  the  degree  to  which  they  withstand  low  temperatures.  Following 
the  severe  cold  weather  of  January,  1922,  observations  were  made  on 
the  various  degrees  of  injury.  Many  trees  that  lost  all  foliage  but 
which  did  not  suffer  injury  to  the  framework  parts  recovered  in  a 
remarkably  short  time.  New  leaves  were  put  out  and  in  some  cases 
bloom,  followed  with  a  small  set  of  fruit  the  same  season.  The  spray- 
ing of  defoliated  trees  with  whitewash  immediately  following  the 
freeze  is  thought  to  have  prevented  sunburn  and  aided  in  recovery. 
Pruning  should  be  delayed  until  all  dying  back  has  ceased ;  cuts  can 
then  be  made  with  certainty.     The  resulting  vigorous  shoots  should 


BUL.  365]  AVOCADO  CULTURE  IN  CALIFORNIA  37 

be  thinned  somewhat,  in  order  to  direct  growth  into  a  smaller  number 
of  well-spaced,  strong  growing  limbs. 

Because  of  the  softness  of  the  heartwood  and  the  readiness  with 
which  it  decays,  large  frost  cracks  and  injured  areas  should  be  care- 
fully cleaned,  disinfected  with  mercuric  chlorid  (corrosive  sublimate) 
solution  of  a  strength  of  1 :1000,  and  painted  over  with  a  waterproof 
covering  such  as  asphaltum  roofing  paint  or  a  rather  soft  grafting 
wax.  Special  attention  should  be  given  such  wounds,  as  decay  sets  in 
readily  and  spreads  rapidly.  Where  large  areas  of  bark  and  wood  are 
killed,  it  is  a  question  whether  or  not  the  resulting  mechanical  weak- 
ness can  ever  be  overcome  sufficiently  to  make  a  satisfactory  tree. 

Frost  injury  may  be  classified  under  three  divisions :  injury  to  the 
blossoms,  injury  to  the  fruit,  and  injury  to  the  tree  itself.  The 
Mexican  varieties  bloom  during  the  winter  and  are  thus  especially 
subject  to  frost  injury  with  the  resulting  loss  of  the  crop,  even  though 
the  trees  themselves  may  not  suffer.  The  Guatemalan  varieties,  on 
account  of  their  later  blooming  period  are  much  less  subject  to  loss  of 
crop  from  frost  injury.  Because  of  its  high  oil  content  the  avocado 
fruit  does  not  readily  freeze.  Heavy  losses  have  occurred,  however, 
due  to  the  freezing  of  the  stems  which  causes  the  fruit  to  drop. 

The  development  of  varieties  which  bloom  after  the  frost  and 
mature  their  crops  in  eight  to  ten  months  will  materially  reduce  losses. 
Several  such  new  varieties  are  now  under  observation. 

Frost  injury  to  the  tree  itself  may  vary  anywhere  from  the  killing 
of  the  young,  tender  growth  to  the  killing  of  the  tree  down  to  the 
ground.  Aside  from  variety,  the  degree  of  injury  depends  largely 
upon  the  physiological  condition  of  the  tree.  In  general,  trees  main- 
tained under  optimum  growing  conditions  enter  the  winter  in  the  best 
condition  to  withstand  cold.  The  maintenance  of  ample  soil  moisture 
is  especially  conducive  to  frost  resistance.  Trees  weakened  from 
insufficient  moisture  are  invariably  less  resistant  and  suffer  more. 
The  practice  of  withholding  water  during  the  fall,  supposedly  to 
harden  off  the  trees,  cannot  be  recommended  as  a  sound  practice. 
Trees  thus  handled  are  ready  to  start  into  growth  again  at  the  first 
rain  which  may  occur  in  the  early  winter,  and  are  in  susceptible  con- 
dition for  frost  injury.  The  best  recommendation  that  can  be  made  is 
to  maintain  favorable  soil  moisture  conditions  throughout  the  growing 
season  and  until  the  beginning  of  the  rainy  reason. 

There  is  a  pronounced  difference  in  frost  resistance  among  the 
three  races  of  avocados.  The  West  Indian  race  is  much  too  tender 
for  planting  in  California  with  the  exception  of  a  few  favored 
localities,  and  even  there  has  rarely  produced  satisfactory  fruits. 


38  UNIVERSITY  OF  CALIFORNIA EXPERIMENT  STATION 

Studies  on  the  relative  freezing  points  of  the  cell  sap  of  the  different 
races  show  that  the  sap  of  this  race  freezes  at  higher  temperatures 
than  do  those  of  the  Guatemalan  and  Mexican  varieties.  Of  these, 
the  Guatemalan  is  the  more  tender.4.  Prior  to  the  freeze  of  1922  it 
was  generally  believed  that  the  Guatemalan  race  was  as  hardy  as  the 
lemon,  and  the  Mexican  as  frost  resistant  as  the  orange.  It  is  evident 
from  many  observations  made  following  this  freeze,  that  the  Guate- 
malan varieties  must  be  considered  for  the  most  part  somewhat  more 
tender  than  the  lemon.  Mexican  varieties,  on  the  other  hand,  were 
observed  in  some  localities  to  be  less  injured  than  neighboring  orange 
trees,  while  in  other  localities  somewhat  more  injured.  Two  varieties 
especially,  proved  to  be  outstandingly  resistant  and  suffered  little 
injury  where  they  had  been  grown  under  good  cultural  conditions. 
These  were  the  Puebla,  a  thin  skinned  Mexican  fruit ;  and  the  Fuerte, 
a  Guatemalan  variety  having  a  leathery  skin  and  which  is  apparently 
a  hybrid  with  a  variety  of  Mexican  origin. 

The  behavior  of  these  and  of  varieties  of  the  Mexican  race  in 
general  throughout  the  entire  state  lends  weight  to  the  belief  that 
varieties  of  the  latter  race  will  play  an  important  part  in  the  develop- 
ment of  the  commercial  varieties.  It  is  certain  that  they  merit  much 
more  attention  than  has  been  accorded  them  in  the  past. 

Seedlings  of  some  of  the  Guatemalan  trees  now  fruiting  in  southern 
California  have  shown  a  hardiness  equal  to  that  of  the  Fuerte,  and 
may  be  of  a  similar  hybrid  origin.  Several  of  these  came  through 
the  freeze  of  1922  unscathed  and  have  commenced  blooming  at  an 
early  age.  One,  at  least,  has  already  produced  superior  fruit.  These 
trees  may  furnish  some  new  varieties  better  suited  climatically  to 
southern  California. 

In  an  industry  that  promises  such  favorable  returns,  frost  protec- 
tion is  deserving  of  more  attention  than  it  has  received.  With  the 
exception  of  higher  hillside  plantings  most  of  the  avocado  orchards  are 
subject  to  periodic  freezing  temperatures.  The  loss  of  the  fruit  is  of 
less  consequence  than  the  injury  to  the  trees.  Adequate  frost  protect- 
ion must  be  considered  a  necessary  feature  of  orchard  management. 
In  a  very  limited  way  various  methods  of  protection  have  been  used 
including  planting  under  lath,  growing  under  tobaco  cloth,  and 
orchard  heating.  Of  these,  the  latter  alone  has  proved  satisfactory. 
Heaters  of  large  fuel  capacity,  sufficient  to  withstand  several  days  of 
cold  weather,  will  be  necessary.  A  heater  to  each  tree  will  doubtless 
prove  advisable. 


4  Harris,  J.  Arthur,  and  Wilson  Popenoe.  Freezing  point  lowering  of  the  leaf 
sap  of  the  horticultural  types  of  Persea  americana.  Jour.  Agr.  Eeseareh  7:  261- 
268.    1916. 


BUL.  365]  AVOCADO  CULTURE  IN  CALIFORNIA  39 


WIND   DAMAGE 

The  avocado  is  subject  to  wind  injury  which  is  manifest  in  breakage 
of  limbs,  in  blowing  off  of  fruit,  and — especially  when  hot,  dry  winds 
occur — in  the  burning  up  of  young  growth  and  the  drying  out  of 
foliage.  The  fruit  may  be  scarred  even  though  not  caused  to  fall ;  this 
materially  reduces  its  saleability,  though  not  always  the  quality. 

Damage  from  wind  prevalence  may  be  reduced  by  the  use  of  lath 
screens,  which  are,  however,  expensive.  Windbreaks  are  a  material 
aid  in  prevention  of  wind  injury,  but  their  use  on  small  plantings  cuts 
down  the  amount  of  available  space  for  trees,  and  increases  the 
amounts  of  water  and  fertilizer  that  must  be  applied  to  maintain  the 
orchard.  The  injurious  effects  to  the  tree  caused  by  excessive  evapora- 
tion may  be  minimized  by  the  maintenance  of  good  moisture  conditions 
in  the  soil  at  all  times  and  the  application  of  additional  water  during 
windy  periods. 

INSECT  PESTS  AND   DISEASES 

The  avocado  in  California  has  been  remarkably  free  from  serious 
insect  pests  and,  until  quite  recently,  from  important  diseases.  Appar- 
ently introduced  free  from  these  hindrances,  it  has  required  some 
years  for  insects  and  diseases  already  established  in  California  to 
adapt  themselves  to  a  new  host  plant.  From  this  point  of  view  the 
insect  and  disease  control  problems  may  be  expected  to  become  increas- 
ingly important  in  the  future. 

Among  the  scale  insects  which  occasionally  infest  the  trees  are  the 
black  scale,  Saissetia  oleae  (Bernard),  the  citrus  red  scale,  Chrysom- 
phalus  aurantii  (Maskell),  the  Spanish  red  scale,  Chrysomphalus 
dictyospermd  (Morgan),  and  mealybugs,  Pseudococcus  spp.  The  usual 
control  method  employed  for  these  pests  is  the  use  of  oil  sprays.  The 
Spanish  red  scale  frequently  attacks  young  trees  in  the  greenhouse  but 
has  not  yet  been  found  on  trees  in  the  field.  Inasmuch  as  it  is  an 
important  pest  of  avocados  and  citrus  trees  in  other  parts  of  the 
world,  its  introduction  and  spread  should  be  carefully  safeguarded. 
The  control  of  mealybugs  is  dependent  to  a  large  degree  on  the  control 
of  the  attending  ants  and  the  use  of  predacious  and  parasitic  insect 
enemies.5 

Of  the  other  insects6  perhaps  the  most  important  are  the  bean 
thrips,  Heliothrips  fasciatus  (Pergande),  and  the  greenhouse  thrips, 


s  Borden,  Arthur  D.  Control  of  the  common  mealybug  on  citrus  in  California. 
U.  S.  Dept.  Agr.  Farmers'  Bui.  1309:  1-10.     1923. 

6  Condit,  I.  J.  Insect  pests  of  the  avocado.  California  State  Comm.  Hort. 
Monthly  Bui.  8  (1) :  27-29.     1919. 


40  UNIVERSITY  OF  CALIFORNIA — EXPERIMENT  STATION 

Heliothrips  balmorrhoidalis  (Bouche),  which  infest  the  fruit  and 
foliage  causing  serious  scarring,  cracking  and  discoloration.  They 
have  been  most  injurious  in  the  coastal  areas,  but  also  occur  generally 
through  the  southern  part  of  the  state.  Dusting  with  a  5  per  cent 
nicotine  dust  will  give  control.  The  branch  and  twig  borer,  Polycaon 
confertus  (Leconte),  frequently  bores  smooth,  round  holes  one-eighth 
inch  in  diameter  and  one-fourth  to  one-half  inch  long  in  the  bud 
axils  or  in  the  forks  of  the  branches.  Sap  collecting  in  the  burrows, 
evaporates  and  produces  white  powdery  masses  over  the  entrance 
concealing  them.  This  beetle  occurs  throughout  the  avocado  growing 
districts  of  the  state  but  is  seldom  sufficiently  numerous  to  cause 
serious  damage.  The  fruit-tree  serica,  Serica  alternata  (Leconte), 
has  been  responsible  for  the  occasional  defoliating  of  trees  in  Ventura 
County,  but  is  not  a  common  pest. 

A  number  of  fungus  diseases  of  the  avocado  have  been  reported, 
two  of  which  attack  the  trunk  or  roots,  and  several  which  affect  the 
fruit.  A  root  disease7  is  caused  by  a  species  of  Pythiacystis,  similar 
to  P.  citrophthera,  which  causes  a  dying  of  the  bark,  indicated  by 
black  areas  from  which  small  beads  of  gum  appear  followed  by  the 
deposition  on  the  surface  of  a  white  powdry  substance.  Conditions 
favorable  for  its  development  are  excessive  moisture  and  poor  drain- 
age, most  commonly  found  in  lath  houses.  The  disease  is  not  at  all 
serious  though  occasionally  large  trees  may  be  attacked.  Dissecting 
out  all  affected  tissue  and  disinfecting  with  bordeaux  paste  has 
proved  a  successful  control  measure.  It  was  formerly  believed  that 
the  avocado  was  immune  to  attacks  of  the  oak  root  or  toad-stool 
fungus,  Armillaria  mellea,  but  within  the  past  five  years  a  number  of 
cases  of  this  disease  on  the  avocado  have  been  reported.  No  entirely 
satisfactory  treatment  is  known,  although  careful  dissection  out  of  all 
the  diseased  tissues  followed  by  thorough  disinfection  appears  to 
materially  retard  its  development. 

In  recent  years  diseases  affecting  the  fruit  have  increased  greatly 
in  seriousness  and  it  is  now  apparent  that  unless  control  measures  are 
developed  for  these  diseases  avocado  growers  must  expect  heavy  losses 
in  some  seasons.  Various  fungi  and  at  least  one  pathogenic  bacterium, 
that  producing  citrus  blast  and  black  pit  of  the  lemon,  have  been 
isolated  from  avocados  decaying  while  still  on  the  trees.  The  effect 
of  some  of  these  organisms  appears  to  be  confined  to  cracking  and 
splitting  of  the  skin,  while  others  seem  also  to  attack  the  flesh  of  the 
fruit.     It  is  highly  important  that  losses  from  these  causes  be  pre- 


7  Fawcett,  H.  S.     A  bark  disease  of  avocado  trees.     California  Avocado  Asso- 
ciation Annual  Report  1916:  152.     1917. 


BUL.  365]  AVOCADO  CULTURE  IN  CALIFORNIA  41 

vented  insofar  as  it  is  possible  to  do  so,  but  their  prevention  must 
await  the  results  of  investigations  now  under  way.  From  a  packing 
house  point  of  view  the  worst  of  these  diseases  are  anthracnose  and  a 
Diplodia  spotting  which  sometimes  pass  through  the  packing  house 
undetected,  only  to  show  up  on  arrival  in  the  markets. 


SOME   FACTORS  AFFECTING  THE  SETTING   OF  SATISFACTORY 

CROPS 

Under  apparently  favorable  environmental  and  cultural  condi- 
tions, it  is  not  uncommon  for  avocado  trees  to  fail  to  bear  satisfactory 
crops.  This  behavior  is  especially  prevalent  with  the  Guatemalan 
varieties  in  the  interior  districts  where  it  often  constitutes  the 
principal  deterrant  to  success.  Even  though  bloom  may  be  produced 
in  abundance  the  young  fruits  very  commonly  fail  to  set,  or  in  the 
event  of  setting,  drop  off  before  development  proceeds  very  far.  On 
the  other  hand,  many  seedling  trees  and  some  budded  trees  have 
failed  to  bloom  regularly,  even  though  well  past  the  usual  bearing 
age.  Moreover,  in  most  varieties  there  is  a  decided  tendency  to 
alternate  bearing.  The  causes  accounting  for  these  unsatisfactory 
conditions  are  not  well  understood.  There  have  been  no  long  con- 
tinued investigations  with  the  avocado  looking  toward  their  solution ; 
such  investigations  are  greatly  needed. 

Pollination. — One  of  the  factors  that  probably  has  much  to  do 
with  the  problem  is  that  of  pollination.  Its  importance  in  other  fruit 
industries  is  well  understood.  The  results  of  investigations  in  Florida 
by  Nirody8  and  in  southern  California  and  Florida  by  Stout9  of  the 
New  York  Botanic  Garden  have  given  valuable  information  on  the 
habits  of  avocado  flowers.    Present  evidence  indicates  that: 

1.  Avocado  flowers  tend  to  open  and  close  in  unison  and  to  open 

and  close  for  two  distinct  periods  at  different  times  during 
the  twenty-four  hours. 

2.  The  pistil  is  almost  always  receptive  only  during  the  first  period 

of  opening;  during  the  second  period  the  pollen  is  shed. 

3.  In  most  varieties  there  are  few  if  any  flowers  open  for  the  first 

time  when  flowers  open  for  the  second  time  are  shedding 
pollen. 


s  Nirody,  B.  S.  Investigations  in  avocado  breeding.  California  Avocado 
Association  Annual  Eeport  1922:  65-78.     1923. 

9  Stout,  A.  B.  A  study  in  cross-pollination  of  avocados  in  southern  California. 
California  Avocado  Association  Annual  Eeport  1922:29-45.     1924.     See  also 

Robinson,  T.  R.,  and  E.  M.  Savage.  Pollination  of  the  avocado.  U.  S.  Dept. 
Agr.  Dept.  Cir.  387:  1-16.    1926. 


42  UNIVERSITY  OF  CALIFORNIA EXPERIMENT  STATION 

4.  Varieties  differ   greatly  in  the  length   of  time  during  which 

flowers  are  open,  and  in  the  time  of  day  when  flowers  open 
both  for  the  first  and  for  the  second  time.  Certain  varieties 
are  shedding  pollen  while  others  have  pistils  ready  for 
pollination. 

5.  In  a  few  varieties  a  considerable  over-lapping  between  the  two 

periods  of  opening  occurs,  making  possible  self-pollination. 

6.  Apparently,  self-incompatability  exists  with  a  number  of  varie- 

ties, even  when  pollen  is  applied  when  the  pistil  is  receptive ; 
this  renders  cross-pollination  necessary. 

7.  The  state  of  the  weather  has  a  decided  effect  upon  the  time  of 

opening,  upon  the  period  over  which  flowers  remain  open, 
and  upon  the  time  and  manner  of  the  shedding  of  pollen. 

On  the  basis  of  their  flower  behavior  Stout  has  classified  all  the 
varieties  studied  thus  far  into  two  general  groups,  those  in  which  the 
flowers  are  open  and  the  pistil  receptive  in  the  forenoon  but  pollen  is 
not  discharged  (Group  A),  and  those  in  which  the  situation  is 
reversed  in  that  the  flowers  are  open  and  the  pistil  in  receptive  con- 
dition in  the  afternoon  but  pollen  is  not  discharged  (Group  B).  In 
both  groups  a  second  opening  of  the  flowers  occurs,  at  which  time  the 
pollen  is  shed.  The  intervening  period  of  about  twenty-four  hours 
during  which  the  flowers  are  closed  separates  the  time  of  maturity  of 
the  sex  organs  in  each  flower. 

GROUP  A  GROUP  B 

Blakeman  Fuerte 

Taft  Linda 

Challenge  Ganter 

Dickenson  Lyon 

Colorado  Panchoy 

Wagner  Queen 

Murrieta  Green  Winslow 

Grande  Winslowson 

Sharpless  Pollock 

Taylor  Trapp 
Manik 
Mayopan 
Waldin 
Collinson 

It  appears  probable,  therefore,  that  more  regular  bearing  of  crops 
may  result  where  plantings  are  made  of  varieties  from  the  two  groups, 
which  should  afford  better  opportunities  for  pollination  than  where 
varieties  of  only  one  group  are  planted.    Since  varietal  compatibilities 


BUL.  365]  AVOCADO  CULTURE  IN  CALIFORNIA  43 

have  not  yet  been  determined  it  appears  desirable  to  use  several 
varieties  from  each  group,  though  observation  has  indicated  that  the 
Dickinson  or  Dutton  and  Fuerte  are  especially  adapted  to  each  other. 
It  is  to  be  hoped  that  self-compatible  varieties  may  be  found  or 
developed,  the  opening  periods  of  whose  flowers  over-lap.  Such 
varieties  would  be  ideal,  at  least  from  the  point  of  view  of  pollination. 

The  bearing  of  crops  by  isolated  trees  in  some  localities  and 
occasionally  by  solid  blocks  of  well  known  varieties,  where  over-lapping 
does  not  ordinarily  occur  is  not  in  conflict  with  the  above  observations. 
It  has  been  pointed  out  by  Stout  that  variable  weather  conditions, 
particularly  abrupt  changes  in  illumination,  temperature,  humidity 
and  wind  exposure  caused  marked  changes  in  the  rather  precise 
periodicity  of  flower  opening  during  clear,  warm,  bright  weather. 
These  changes  result  in  increasing  the  amount  and  prolongation  of 
over-lapping,  frequently  increasing  the  opportunity  for  self-pollina- 
tion many  fold.  The  more  satisfactory  setting  of  fruits  of  some  varie-" 
ties  near  the  coast  where  atmospheric  conditions  are  subject  to  both 
continual  and  frequent  sudden  changes  is  partially  explained,  in  all 
probability,  by  this  increased  over-lapping.  The  unusually  heavy 
crop  on  trees  of  almost  all  varieties  in  the  1923-4  season  is  also 
undoubtedly  due  in  a  large  measure  to  the  abnormal  weather  condi- 
tions obtaining  throughout  the  blooming  period  in  1923. 

Bud  Selection. — It  has  long  been  known  that  the  avocado  is  subject 
to  bud  variation.  Black  Ganter  fruits  are  consistently  produced  on 
one  limb  of  a  large  tree  in  Whittier.  Round  forms  of  the  Fuerte  have 
been  discovered  on  standard  trees.  Such  occurrences  indicate  the 
desirability  of  using  care  in  the  selection  of  bud  wood.  In  the  early 
days  of  the  industry  buds  were  taken  from  any  kind  of  wood  available 
and  from  any  source  convenient,  with  resulting  wide  variation  in  the 
type  and  quality  of  trees  produced.  At  the  present  time  nurserymen 
are  giving  very  careful  attention  to  the  selection  of  wood  from  thrifty, 
good  producing  trees,  and  the  type  of  nursery  trees  now  being  grown 
testifies  to  the  value  of  this  practice.  Some  work  has  been  started 
along  the  lines  of  tree  record  keeping  with  the  purpose  of  locating 
high  producing  parent  trees.  Such  work  will  be  handicapped  until 
there  is  a  sufficient  number  of  trees  growing  under  identical  orchard 
conditions  to  eliminate  environmental  factors  and  make  detection  of 
inherent  variations  certain. 

June  Drop. — Severe  shedding  of  the  young  fruits  has  been  noted 
during  hot  weather  and  is  not  an  uncommon  cause  of  the  low  yields 
sometimes  obtained.     This  trouble  is  especially  severe  in  the  navel 


44  UNIVERSITY  OF  CALIFORNIA EXPERIMENT  STATION 

orange.  Investigations  by  Coit  and  Hodgson10  have  shown  that  it  is 
ordinarily  caused  by  the  excessive  evaporation  that  takes  place  from 
the  leaf  surface  during  periods  of  hot  or  dry  atmospheric  conditions. 
The  root  system  is  unable  to  supply  moisture  fast  enough  under  such 
conditions  and  water  is  withdrawn  from  the  young  fruits  to  make  up 
the  deficiency,  with  the  result  that  they  are  weakened  and  drop  off. 
A  spring  cover  crop,  grown  to  furnish  a  good  ground  covering  by 
June,  has  been  found  under  certain  conditions  to  cut  down  the  tem- 
perature materially  within  the  orchard  and  reduce  the  drop.  Purple 
vetch  planted  early  in  March  has  given  the  best  growth  of  any  crop 
yet  tried  for  this  purpose.  The  extent  to  which  this  factor  affects  the 
avocado  has  not  yet  been  determined,  but  in  all  probability  it  has  an 
important  bearing  on  the  failure  to  secure  satisfactory  crops. 

Rootstocks. — The  importance  of  desirable  rootstocks  has  already 
been  mentioned.  Sufficient  attention  to  securing  the  most  congenial 
•stocks  has  not  been  given  in  the  past.  Certain  varieties  make  very 
poor  unions  with  stocks  at  present  used  and  fail  to  make  satisfactory 
trees.  In  this  connection  it  is  interesting  to  note  a  reaction  observed 
in  the  W.  A.  Spinks  orchard  at  Duarte.  A  number  of  large  Harman 
trees  were  budded  over  to  the  Murrieta  variety,  and  failing  to  make 
satisfactory  growth,  were  topped  and  budded  to  another  variety. 
Two  or  three  of  the  Murrieta  buds  were  overlooked  and  when  the 
vigorous  growing  buds  began  to  develop  a  thrifty  top,  the  Murrieta 
buds  were  stimulated  into  active  growth,  put  out  strong  branches,  and 
have  since  borne  good  crops. 

Studies  with  citrus  and  deciduous  fruits  have  indicated  the  close 
relation  to  vigor  and  production  that  congeniality  of  stock  and  scion 
maintain.  This  phase  of  development  of  satisfactory  yielding  trees 
awaits  thorough  investigation. 

Girdling. — Girdling  has  been  resorted  to  as  a  means  of  stimulating 
fruit  production  on  otherwise  barren  trees.  Successful  results  have 
been  obtained  in  some  cases  and  in  others  none  whatever.  The  Taft 
variety  which  has  been  conspicuous  for  its  delay  in  coming  into  bear- 
ing has  been  the  object  of  such  experimentation  more  than  any  other. 
A  number  of  growers  have  succeeded  in  getting  fruit  to  set  in  abun- 
dance on  girdled  limbs  while  the  rest  of  the  tree  failed  to  produce. 
Girdling  is  best  done  in  October.  A  ring  of  bark  varying  from  an 
eighth  to  a  quarter  of  an  inch  in  width  is  removed  usually  near  the 


10  Coit,  J.  Eliot,  and  Eobert  W.  Hodgson.  An  investigation  of  the  abnormal 
shedding  of  young  fruits  of  the  Washington  navel  orange.  Univ.  of  California 
P.ubl.  in  Agr.  Science  3:  283-368.     1919. 


BUL.  365]  AVOCADO  CULTURE  IN  CALIFORNIA  45 

base  of  the  limb  ;  a  ring  of  this  size  will  readily  heal  over.  Apparently 
the  downward  flow  of  sap  is  checked  and  the  storage  of  food  materials 
stimulates  fruit  production.  Girdling  is  still  largely  in  the  experi- 
mental stage,  however,  and  cannot  be  considered  as  the  solution  of  the 
many-sided  problem  of  rendering  barren  trees  fruitful.  It  has  the 
disadvantages  of  lowering  the  resistance  to  frost  of  the  limb  girdled, 
and  of  weakening  the  roots  through  subjecting  them  to  a  period  of 
partial  starvation. 

MARKETING 

Avocado  production  in  California  did  not  reach  the  point  where 
marketing  problems  became  acute  until  within  the  past  three  years. 
Prior  to  that  time  the  production  was  relatively  so  small  that  the  local 
markets  were  able  to  absorb  the  crop  at  very  satisfactory  prices. 
Price  levels  were  in  fact  too  high  to  favor  any  appreciable  extension 
in  the  use  of  the  fruit.  These  high  prices,  however,  stimulated  greatly 
the  planting  of  avocado  orchards  to  the  extent  that  for  some  years 
past  it  has  been  evident  that  the  time  was  not  far  removed  when 
production  would  increase  so  greatly  as  to  render  it  necessary  for 
the  growers  to  concern  themselves  with  marketing  problems. 

In  anticipation  of  this  situation  the  California  Avocado  Associ- 
ation some  years  ago  undertook  a  study  of  the  marketing  problem, 
with  the  result  that  in  1921  an  arrangement  was  made  whereby  the 
fruit  was  marketed  through  a  large  fruit  and  vegetable  marketing 
agency  with  selling  agents  in  many  of  the  principal  markets.  The 
crop  was  marketed  on  a  commission  basis,  with  the  understanding 
that  some  effort  would  be  made  to  introduce  the  fruit  into  new 
markets  and  to  advertise  it.  The  members  reserved  the  right  to 
market  such  fruit  as  they  desired  locally.  This  arrangement  did  not 
prove  to  be  very  satisfactory,  and  within  a  year  or  two  the  increase 
in  production  was  such  as  to  indicate  the  need  for  increased  marketing 
facilities. 

With  the  support  and  financial  assistance  of  the  California 
Avocado  Association,  the  California  Avocado  Growers'  Exchange,  a 
cooperative  marketing  agency,  was  organized  in  February  1924.  In 
1927  the  name  of  this  organization  was  changed  to  the  Calavo  Growers 
of  California.  The  plan  of  organization  followed  was  similar  in  many 
respects  to  that  employed  by  the  citrus  growers  in  that  the  organiza- 
tion is  a  non-stock,  non-profit,  cooperative  agency,  with  a  board  of 
directors  composed  of  elected  representatives  from  the  principal 
avocado  producing  districts  and  a  limited  number  of  directors  elected 


46 


UNIVERSITY  OF  CALIFORNIA EXPERIMENT  STATION 


at  large.  A  centrally  owned  and  managed  packing  house  was  estab- 
lished at  Los  Angeles,  and  more  recently  several  additional  houses 
have  been  established  at  other  central  points. 

Considering  the  problems  presented  in  introducing  and  popular- 
izing a  new  and  unique  fruit,  and  the  limited  funds  which  have 
been  available,  this  organization  has  been  remarkably  successful  in 
marketing  the  crops  of  its  members.  The  percentage  of  the  crop  it 
handles  has  increased  greatly  since  the  time  of  its  organization,  and 


Fig.  13. — The  fruit  is  packed  in  excelsior  in  one  and  two-layer  boxes  for 
shipment.  The  above  shows  fruit  as  received  from  grower  in  lug  boxes.  Lower 
left,  two-layer  lug  box  packed  and  topped.  Above  it,  one-layer  crate  holding  one 
dozen  fruits. 


it  is  at  the  present  time  by  all  odds  the  dominant  factor  in  the  Cali- 
fornia avocado  industry.  It  had  scarcely  been  organized  when  the 
expected  increase  in  production  materialized  and  the  necessity  arose 
of  immediately  developing  outlets  for  the  fruit  in  the  markets  of 
eastern  United  States.  This  has  required  costly  and  sustained  effort 
on  the  part  of  the  producers,  but  it  was  indeed  fortunate  that  the 
organization  was  available  for  the  task.  While,  necessarily,  progress 
has  been  slow,  it  has  been  able  to  extend  the  market  outlets  rapidly 
enough  to  absorb  the  surplus  over  the  local  requirements,  which  con- 
sist mainly  of  the  markets  in  Los  Angeles  and  San  Francisco.    As  a 


BUL.  365]  AVOCADO  CULTURE  IN   CALIFORNIA  47 

consequence  price  levels  have  continued  to  be  high,  much  higher  in 
fact  than  can  probably  be  expected  in  the  future  when  the  production 
is  several  times  what  it  is  today. 

Through  the  efforts  of  this  marketing  agency,  many  important 
improvements  have  been  brought  about  in  the  industry,  such  as  the 
adoption  of  a  maturity  standard,  the  enforcement  of  laws  against 
fruit  stealing,  the  initiation  of  much  needed  investigations,  and  others. 

For  the  dual  purpose  of  advertising  California  avocados  and  the 
brand  of  the  marketing  organization,  the  first  grade,  mature  fruits 
of  selected  varieties  sold  by  the  Calavo  Growers  of  California  are 
stamped  with  the  word  Calavo,  the  term  being  derived  from  the 
abreviation  and  combination  of  the  two  words  California  and  avocado. 
Other  grades  have  also  been  established,  and  in  all  cases  the  grade  is 
stamped  on  the  fruit.  Each  grade  has  certain  requirements  as  to 
size,  color,  freedom  from  blemishes  and  fat  content,  the  latter  varying 
with  the  variety. 

Official  standard  containers  for  avocados  have  not  been  adopted  as 
yet,  awaiting  the  results  of  experience  in  packing  and  marketing  the 
fruit.  On  account  of  the  susceptibility  of  the  fruit  to  bruising,  it  is 
packed  in  wood  or  paper  excelsior,  and  rarely  or  never  more  than  two 
layers  deep.  The  thirty-pound  lug  box  packed  with  two  layers  of 
fruit  is  most  commonly  used,  though  several  one-layer  packs  are  also 
employed.  All  operations  incident  to  the  preparation  of  the  fruit  for 
market  are  performed  by  hand,  which  is  necessary  on  account  of  the 
variation  in  shape  of  fruit  in  the  different  varieties  and  the  marked 
susceptibility  of  the  fruit  to  bruising.  These  operations  include 
grading,  sizing,  weighing,  stamping  and  packing.  The  fruit  is  packed 
unwrapped. 

Avocados  to  be  sold  on  the  local  markets  are  held  in  storage  at 
room  temperature  until  softened  sufficiently  for  consumption  within 
a  few  days.  If  storage  for  longer  periods  is  required  the  fruit  is 
held  in  cold  storage  chambers  at  40  to  45  degrees  Fahr.,  experience 
having  shown  that  the  fruit  keeps  best  in  this  temperature  range. 
Avocados  have  been  successfully  stored  for  more  than  two  months. 
Fruit  to  be  shipped  to  eastern  markets  is  packed  soon  after  receipt 
from  the  orchards  and  is  held  in  storage  in  the  markets  until  ready 
for  consumption,  unless  it  has  softened  sufficiently  en  route,  in  which 
case  it  is  sold  immediately. 

In  recent  years  shipment  of  the  fruit  to  eastern  markets,  mainly 
Chicago  and  New  York,  has  become  of  increasing  importance  as  a 
means  of  relieving  the  local  markets  of  surplus  supplies,  and  the 
amount  of  the  crop  shipped  out  of  the  state  has  increased  rapidly. 


48  UNIVERSITY  OF  CALIFORNIA EXPERIMENT  STATION 

Whereas,  a  few  years  ago  only  a  few  hundred  boxes  of  fruit  were 
shipped  to  eastern  markets,  in  1927  of  approximately  one  million 
pounds  of  fruit  handled  by  the  Calavo  Growers  of  California,  nearly 
two-thirds  was  shipped  out  of  the  state. 

Most  of  the  shipments  in  the  past  have  been  by  express,  though 
experience  in  the  past  year  or  two  has  shown  that  if  properly  handled 
the  fruit  stands  up  satisfactorily  under  fast  freight.  Carlot  shipments 
have  been  made  on  a  number  of  occasions  during  the  past  two  years. 
It  is  expected  that  in  the  future  mixed  car  shipments  will  play  an 
important  part  in  the  distribution  of  the  avocado  crop.  Experimental 
shipments  by  steamboat  via  the  Panama  Canal  to  New  York  have 
shown  that  the  fruit  successfully  withstands  the  long  trip,  providing 
it  is  properly  selected  and  prepared  for  shipment. 

California  grown  avocados  must  meet  the  competition  of  Florida 
and  West  Indian  fruits,  which  ripen  during  the  summer  and  fall 
months,  when  there  is  an  abundance  of  other  fruits  of  other  kinds; 
accordingly  the  price  is  lower  than  at  any  other  time  of  the  year. 
The  best  market  is  to  be  had  during  the  winter  months,  and  it  is  this 
market  that  is  of  particular  interest  to  the  California  grower,  as  he 
already  has  varieties  that  mature  at  this  season.  With  the  establish- 
ment of  the  avocado  as  an  important  article  of  food  rather  than  a 
luxury,  an  all-year-round  demand  will  be  created.  Future  commercial 
production  must  take  this  condition  into  account.  At  the  present  time 
there  is  sufficient  variation  in  season  among  the  varieties  in  California 
to  furnish  ripe  avocados  for  every  month  of  the  year.  It  would  seem 
desirable,  however,  for  the  growers  in  the  various  avocado  producing 
sections  to  take  advantage  of  the  natural  ripening  seasons  in  their 
respective  districts  in  so  far  as  this  is  practicable.  Thus,  it  would 
seem  best  for  the  growers  in  the  early  ripening  districts  to  grow 
largely  the  early  ripening  varieties  and  for  the  growers  in  the  late 
sections  to  concentrate  mainly  on  the  late  varieties.  For,  obviously, 
an  early  ripening  variety  grown  in  a  late  district  is  neither  early  nor 
late  and  consequently  cannot  possibly  command  any  premium  on  this 
basis.  There  may  be  other  factors  of  sufficient  importance  to  warrant 
the  growers  in  some  sections  ignoring  the  above  mentioned  consider- 
ations, but  in  general  it  is  believed  they  should  be  adhered  to. 

The  place  of  the  thin-skinned  Mexican  fruit  on  the  commercial 
market  has  been  more  or  less  problematical.  The  fruit  is  finer  in 
flavor,  and  often  in  quality,  than  many  of  the  larger  Guatemalan 
fruits.  It  comes  on  the  market  at  a  good  time  of  the  year  and  can 
be  shipped  very  satisfactorily  if  given  a  little  extra  care.  Objections 
to  the  small  size  of  most  varieties  of  this  group  can  be  overcome  by 


BUL.  365]  AVOCADO  CULTURE  IN  CALIFORNIA  49 

the  introduction  of  large-sized  varieties  known  to  exist  elsewhere 
(fig.  14).  Some  of  these  are  now  under  trial.  For  local  markets  and 
for  home  use  they  have  a  very  definite  place.  No  general  prediction 
can  be  made  as  to  their  future  commercially,  until  the  market  has  been 
exploited  and  the  tastes  of  consumers  determined. 


Fig.  14. — Tamayo  avocado  (S.  P.  I.  54270).  A  large-fruited,  thin-skinned 
variety  of  the  Mexican  race  discovered  by  Wilson  Popenoe  in  the  Chota  Valley, 
Ecuador.     The  fruits  weigh  as  high  as  18  ounces. 

The  discovery  of  these  large-fruited  varieties  in  Ecuador  is  of  particular 
promise  for  the  expansion  of  the  area  in  California  in  which  the  avocado  may 
become  commercially  profitable.     (Photo  by  Popenoe.) 


50  UNIVERSITY  OF  CALIFORNIA EXPERIMENT  STATION 

Marketing  experience  indicates  thus  far  that  in  general  there  is  a 
preference  for  medium  sized  fruits,  weighing  from  eight  to  fourteen 
ounces,  although  there  is  a  limited  demand  for  the  large  fruited 
varieties.  Color  appears  to  be  less  important  than  size  though  the 
green  fruited  varieties  seem  to  be  more  in  demand  than  the  colored 
sorts.  The  Mexican  varieties  have  not  met  with  favor  in  the  eastern 
markets  though  they  sell  well  locally  and  in  some  of  the  southwestern 
states.  Of  all  the  varieties  shipped  in  quantity  to  the  eastern  markets 
the  Fuerte  and  Taft  have  consistently  met  with  the  best  reception. 

The  subject  of  varieties  will  be  discussed  in  detail  in  another 
section,  but  it  should  be  mentioned  here  that  adherence  to  a  relatively 
small  number  of  standard  varieties  is  of  importance  to  the  develop- 
ment of  satisfactory  markets.  The  work  of  the  Committee  for  the 
Registration  and  Classification  of  Varieties  of  the  California  Avocado 
Association  has  already  resulted  in  considerable  progress  in  this 
direction. 

RACES   AND   VARIETIES 

As  previously  indicated  there  are  three  general  groups  of  avocados 
grown  in  the  United  States,  for  convenience  loosely  termed  the 
West  Indian,  Guatemalan,  and  Mexican  races,  though  not  strictly 
separate  horticultural  races  in  the  technical  sense  of  the  term.  Of 
these  three  races,  two  only  are  of  commercial  importance  in  California 
— the  Mexican  and  the  Guatemalan.  Popenoe11  has  classified  these 
groups  as  follows : 

1.  Leaves  anise-scented;  skin  of  fruit  thin  (rarely  more  than  %2 
inch  in  thickness).    Persea  drymifolia.    Mexican  Race. 

2.  Leaves  not  anise-scented;  skin  of  fruit  thicker  (from  %2  to  Vi 
inch  in  thickness ) .    Persea  americana. 

(a)  Fruit  summer  and  fall  ripening;  skin  usually  not  more  than 
y1G  inch  thick,  leathery  in  texture.    West  Indian  Race. 

(6)  Fruit  winter  and  spring  ripening;  skin  y16  to  %  inch  thick, 
woody  in  texture.    Guatemalan  Race. 

At  least  one  variety  intermediate  in  form  between  the  Guatemalan 
and  Mexican  races  has  appeared — the  Fuerte,  an  apparent  hybrid 
between  these  two  groups.  Other  intermediate  forms  found  in  Central 
America  and  Mexico  are  at  the  present  time  unclassified. 

The  West  Indian  race  is  unsuited  climatically  to  California  con- 
ditions, as  evidenced  by  the  failure  of  the  plantings  tried  in  the  past, 


11  Popenoe,  Wilson.     Manual  of  tropical  and  subtropical  fruits,  p.   66.     The 
Macmillan  Co.,  New  York.     1920. 


Bul.  365] 


AVOCADO   CULTURE  IN   CALIFORNIA 


51 


5 


52  UNIVERSITY  OF  CALIFORNIA EXPERIMENT  STATION 

and  may  be  disregarded  as  far  as  its  economic  importance  in  this 
state  is  concerned.  Belonging  as  they  do  to  two  different  species, 
the  important,  outwardly-evident,  botanical  differences  serve  to  differ- 
entiate the  Guatemalan  and  Mexican  races  horticulturally.  The  leaves 
of  the  Mexican  race  are  usually  smaller  than  those  of  the  Guatemalan, 
and  are  sharper  at  the  apex.  They  have  the  characteristic  anise  odor 
when  crushed  which  is  entirely  lacking  in  the  Guatemalan  race.  This 
property  is  also  characteristic  of  the  immature  Mexican  fruits.  The 
fruits  of  the  Mexican  race  are  smaller,  rarely  reaching  a  pound  in 
weight,  are  smooth,  dark  green  to  purple  in  color,  and  often  glossy. 
They  mature  usually  from  August  to  December  from  nine  to  ten 
months  after  blooming.  The  seed  is  commonly  larger  in  proportion 
to  the  edible  part  of  the  fruit  than  that  of  the  Guatemalan.  The  two 
seed  coats  are  thin,  sometimes  closely  united  and  adhering  to  the  coty- 
ledons, and  sometimes  separating.  The  flowers  appear  during  the 
winter  and  early  spring,  and  are  subject  to  frost  injury  in  severe 
winters.  Occasionally  late  flowers  appear  and  furnish  a  light  second 
crop  in  the  early  spring. 

The  fruit  of  the  Guatemalan  race  is  large,  averaging  from  12  to  20 
ounces,  some  varieties  attaining  a  weight  of  more  than  three  pounds. 
It  varies  in  color  from  green  to  purplish  or  reddish  black.  The  surface 
while  sometimes  fairly  smooth,  is  usually  rough  and  somewhat  warty 
and  coasely  granular  in  texture.  The  seed  fits  tightly  into  the  cavity, 
its  seed  coats  are  thin,  united,  and  adherent  to  the  cotyledons  through- 
out. The  flowers  appear  later  than  those  of  the  Mexican  race,  usually 
after  most  danger  from  frost  is  past.  The  fruit  matures  from  twelve 
to  eighteen  months  after  the  blossoming  season. 

Many  varieties  of  both  the  Guatemalan  and  the  Mexican  groups 
are  fruiting  in  California  at  the  present  time — the  number  exceeds 
two  hundred.  Because  of  their  greater  resistance  to  cold,  the  Mexican 
varieties  enjoy  a  much  wider  range  of  planting.  In  choosing  varieties 
for  commercial  planting  certain  general  characteristics  are  to  be 
desired  in  both  the  tree  and  the  fruit.  The  tree  itself  must  be  adapted 
to  the  location  selected.  It  should  be  a  hardy  and  vigorous  grower, 
forming  a  well  balanced  head  capable  of  carrying  good  sized  crops 
without  breakage.  It  should  be  readily  propagated  and  easily  handled 
in  the  nursery.  It  should  produce  sufficiently  good  crops  consistently, 
to  be  commercially  profitable,  and  should  come  into  bearing  at  a 
reasonably  early  date.  Varieties  that  have  come  into  bearing  at  too 
early  a  period,  however,  have  a  tendency  to  expend  their  energies  in 
flowering  and  premature  production  at  the  expense  of  tree  develop- 
ment.    The  first  few  years  of  the  life  of  any  fruit  tree  should  be 


Bul.  365] 


AVOCADO  CULTURE  IN   CALIFORNIA 


53 


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54  UNIVERSITY  OF  CALIFORNIA EXPERIMENT  STATION 

primarily  devoted  to  the  building  up  of  a  strong  tree  capable  of  sus- 
tained production  over  a  long  period  of  years  rather  than  to  the  early 
production  of  fruit. 

The  length  of  time  between  blooming  period  and  maturity  is  also 
an  important  consideration.  Most  of  the  thin-skinned  fruits  mature 
from  nine  to  twelve  months  after  blooming;  on  the  other  hand  few 
of  the  Guatemalans  mature  under  fourteen  months,  several  requiring 
eighteen.  Two  of  the  newer  Guatemalan  varieties — the  Ward  and  the 
Dorothea — bloom  in  the  spring  and  mature  their  fruit  in  the  fall  and 
winter  of  the  same  year.  In  developing  new  varieties  this  question 
is  one  that  should  receive  consideration. 

Many  varieties  now  fruiting  in  southern  California  have  been 
noted  to  have  a  more  or  less  pronounced  habit  of  alternate  bearing. 
Popenoe  reports  this  condition  quite  general  among  the  avocados  in 
Guatemala.  Thinning  of  fruit  during  the  heavy  producing  years  may 
aid  in  maintaining  a  more  uniform  annual  production.  No  experi- 
ments have  been  conducted  with  the  fruit  along  this  line. 

The  market  demands  are  important  in  considering  the  fruit  itself. 
A  medium-sized  fruit,  attractive  in  color,  uniform  in  shape  and  readily 
packed,  of  good  quality  and  pleasing  flavor,  fits  the  market  require- 
ments at  the  present  time.  The  seed  should  not  be  large  and  should 
preferably  be  tight  in  the  cavity.  To  meet  the  highest  prices  the  fruit 
should  mature  during  the  winter  and  early  spring  months;  at  this 
season  of  the  year  less  competition  is  met  with  other  kinds  of  fruits 
and  with  avocados  imported  from  the  West  Indies. 

The  matter  of  selecting  varieties  is  one  of  considerable  perplexity. 
The  industry  has  been  fortunate  in  its  early  history,  in  having  an 
active  growers'  organization,  the  California  Avocado  Association, 
working  in  its  interests.  The  Association  early  organized  a  Committee 
for  the  Registration  and  Classification  of  Varieties,  whose  duty  it  has 
been  to  study  the  behavior  of  the  different  varieties  over  a  period  of 
years  and  to  make  recommendations  according  to  its  observations. 
The  lists  of  recommended  varieties  prepared  by  this  committee  afford 
the  safest  guide  to  planting  at  the  present  time.  That  these  lists  will 
be  revised  from  time  to  time  is  certain;  numerous  changes  have  been 
made  in  the  past  as  knowledge  has  been  gained  by  experience.  The 
commercial  varieties  of  the  future  may  be  largely  different  from  those 
of  the  present.  The  recommendations  offered  represent  the  concensus 
of  opinion  of  the  best  growers  at  the  present  time. 

The  history  of  avocado  culture  in  California  has  been  an  almost 
continual    procession    of    new    varieties    as    seedlings    or   introduced 


Bul.  365] 


AVOCADO   CULTURE  IN   CALIFORNIA 


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56  UNIVERSITY  OF  CALIFORNIA EXPERIMENT  STATION 

varieties  have  come  into  bearing  and  have  been  ardently  promoted  by 
their  enthusiastic  developers  or  introducers.  Many  varieties  have 
been  propagated  and  distributed  prematurely.  Others  have  been 
unwisely  exploited  before  testing.  The  result  is  that  there  are  many 
named  varieties  which  have  already  been  discarded  and  many  more 
which  should  and  will  be  abandoned  in  the  future. 

Descriptions  of  the  principal  commercial  varieties  and  of  the  most 
promising  of  the  not  yet  proven  varieties  are  given  below.  Allowance 
should  be  made  for  normal  variation  in  the  size  of  the  fruit  and  in 
the  ripening  season  which  differs  markedly  in  different  sections. 


RECOMMENDED  COMMERCIAL  VARIETIES 

Fuerte  (fig.  15). — At  the  present  time  only  one  variety  is  consid- 
ered worthy  of  unqualified  recommendation  for  commercial  planting. 
Form  pyriform  (not  necked)  to  oblong;  size  below  medium  to  above 
medium;  weight  10  to  16  ounces,  length  4  to  4%  inches,  greatest 
breadth  2%  to  2%  inches;  base  pointed;  the  stem  inserted  obliquely 
in  a  small  shallow  cavity ;  apex  obliquely  flattened,  depressed  around 
the  stigmatic  point ;  surface  pebbled,  sometimes  slightly  wrinkled 
around  the  stem,  dull  green,  with  numerous  small  yellow  dots;  skin 
about  y24  inch  thick,  separating  readily  from  the  flesh,  pliable  and 
leathery  in  texture ;  flesh  rich  cream  yellow  in  color,  greenish  near 
the  skin,  of  smooth,  buttery  texture,  and  very  rich  flavor;  quality 
excellent ;  seed  medium,  tight  in  cavity,  seed  coats  closely  surrounding 
cotyledons.  Season  November  to  June  in  southern  California. 
(Popenoe.) 

Originated  at  Atlixco,  state  of  Puebla,  Mexico ;  introduced  into 
California  in  1911.  The  tree  is  unsually  vigorous,  hardy  and  pro- 
ductive. Its  season  of  ripening  is  exceptionally  long.  The  fruit  con- 
tains 30%  of  oil,  is  of  fine  flavor  and  quality.  This  variety  and  the 
Puebla  described  below,  were  the  two  outstandingly  hardy  varieties 
on  the  recommended  list  of  the  Avocado  Association  that  emerged 
from  the  severe  cold  wave  of  1922  with  comparatively  little  injury. 
The  Fuerte  is  apparently  a  natural  hybrid  between  the  Guatemalan 
and  Mexican  races,  though  final  proof  of  this  assumption  is  yet  to  be 
made.     It  partakes  of  the  characteristics  of  both  races. 


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58  UNIVERSITY  OF  CALIFORNIA — EXPERIMENT  STATION 


VARIETIES  OF   MERIT,   CANDIDATES    FOR   COMMERCIAL   RATING 

Puebla  (fig.  16). — Form  obovoid,  slightly  oblique;  size  below 
medium  to  medium,  weight  8  to  10  ounces,  length  3%  inches,  greatest 
breadth  2%  inches ;  base  obliquely  flattened,  the  stem  inserted  slightly 
to  one  side  in  a  small  shallow  cavity ;  apex  obliquely  flattened  but  not 
prominently  so;  surface  smooth,  glossy,  deep  maroon-purple  in  color, 
with  numerous  reddish  dots ;  skin  less  than  %2  inch  thick,  easily  peeled 
from  the  flesh,  firm  in  texture ;  flesh  rich  cream  yellow  near  the  seed, 
changing  to  pale  green  near  the  skin,  buttery  in  texture,  and  of  rich 
nutty  flavor;  quality  very  good,  seed  medium  to  large,  tight  in  the 
cavity,  with  both  seed  coats  adhering  closely  to  the  cotyledons.  Season 
December  to  February  in  southern  California.     (Popenoe.) 

Originated  at  Atlixco,  state  of  Puebla,  Mexico ;  introduced  and  first 
propagated  in  California  in  1911.  The  tree  is  exceptionally  hardy  and 
vigorous,  and  well  balanced  in  form.  It  fruits  later  in  the  season 
than  most  others  of  the  Mexican  race.  Oil  content  26.45%.  Mex- 
ican race. 

Queen  (fig.  17). — Fruit,  oblong-pyriform,  large,  5x/2  inches  long, 
weighing  1%  pounds;  skin  rough,  deep  purple  in  color,  thick  and 
woody ;  flesh  rich  clear  yellow,  dark  green  near  skin,  free  from  fiber ; 
flavor  rich,  quality  very  good;  seed  very  small  and  tight  in  cavity. 
Season  May  to  October. 

The  variety  was  imported  by  E.  E.  Knight  from  the  highlands 
of  Guatemala.  It  is  a  vigorous  but  spreading  grower,  rather  tender, 
and  should  be  planted  only  in  the  warmest  sections.  The  tree  bears 
very  good  crops.    Guatemalan  race. 

Taft. — Fruit  pyriform  in  shape;  size  medium,  weight  14  to  24 
ounces;  skin  medium  in  thickness,  slightly  rough,  green.  Seed 
medium.  Flesh  cream  to  golden  yellow,  flavor  rich,  quality  excellent. 
Fiber  very  slight. 

Originated  on  place  of  C.  P.  Taft,  Orange,  Calif.,  in  1900. 

Tree  vigorous  but  usually  slow  to  come  into  bearing;  this  is  the 
chief  objection  to  this  variety.  Especially  adapted  to  the  coastal 
districts.    Season,  May  to  November.    Guatemalan  race. 

Nabal  (fig.  18).— Number  15  of  the  U.  S.  Dept.  of  Agriculture 
introductions  by  Popenoe  in  1917  from  Antigua,  Guatemala  (S.  P.  I. 
No.  44439).  Fruit  almost  round,  weight  16  to  20  ounces.  Smooth, 
green.  Seed  rather  small.  Flavor  exceptionally  good  and  quality 
excellent.  A  good  grower  and  heavy  and  consistent  bearer.  Season, 
May  to  July,  This  variety  is  undoubtedly  one  of  the  most  promising 
of  the  Department  of  Agriculture  introductions.    Guatemalan  race. 


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60  UNIVERSITY  OF  CALIFORNIA EXPERIMENT  STATION 


VARIETIES   SUGGESTED    FOR   AMATEUR    COLLECTIONS   AND 
EXPERIMENTAL  PLANTINGS 

Varieties  marked  with  the  asterisk  (*)  are  especially  recommended. 

Anaheim  (fig.  19.) — Originated  on  place  of  E.  C.  Dutton,  West 
Anaheim.  Tree  tall  and  slender.  Fruit  elliptical;  18  to  21  ounces, 
rough,  green,  glassy.  Seed  medium  to  small.  Season,  June  to  Sep- 
tember.   Guatemalan  race. 

Benik* — Introduced  by  Popenoe  from  Antigua,  Guatemala  as 
No.  21  in  1917  (S.  P.  I.  No.  44626).  Fruit  pear-shaped;  20  ounces, 
rough,  maroon-purple.  Seed  small.  Season,  May  to  August.  Guate- 
malan. 

Calient e. — Introduced  from  Mexico  by  M.  Garcia  of  Duarte,  Cali- 
fornia. Fruit  long-pyriform,  necked;  5  to  10  ounces,  smooth,  glassy, 
deep  mahogany-red.  Seed  medium.  Season,  October  to  December. 
Mexican. 

Cant  el. — Another  of  the  Popenoe  introductions  from  Antigua. 
Number  28  (S.  P.  I.  No.  44783).  Fruit  round,  16  ounces,  surface 
pebbled,  green.  Seed  very  small.  Season,  August  and  September. 
Guatemalan. 

Carlsbad* — Probably  identical  to  the  old  Stephens  No.  2  at  Monte- 
bello.  Fruit  pyriform,  16  ounces,  smooth,  mahogany-purple.  Flavor 
very  good.  Prolific.  Seed  rather  large.  Season,  March  to  May. 
Guatemalan. 

Colorado. — Sometimes  known  as  Purple  Murrieta.  Originated  at 
Los  Angeles  about  1901.  Fruit  oval,  14  to  18  ounces,  slightly  rough, 
purple  with  brown  spots.  Seed  medium.  April  to  August.  Hard  to 
propagate  but  top-works  well.     Guatemalan. 

Dickinson  (fig.  20). # — Originated  in  Los  Angeles  about  1899. 
Fruit  oval  to  almost  pyriform,  9  to  14-  ounces,  very  rough,  dark 
purple.    May  to  October.    Guatemalan. 

Dorothea. — A  seedling  from  the  Miller  tree  at  Hollywood.  Fruit 
obovate,  8  to  12  ounces,  smooth,  light  green.  Seed  medium  to  large. 
Season,  November  to  February.  Thought  to  be  a  Guatemalan- 
Mexican  hybrid. 

Duke* — Originated  at  Sunnyslope  nursery  near  Wyandotte,  Cali- 
fornia, in  1912.  Fruit  pyriform,  8  to  12  ounces,  green.  Seed 
generally  tight  in  cavity.     Season,  October  and  November.    Mexican. 

Dutton. — Originated  at  Anaheim  in  1910.  Fruit  pyriform,  16 
ounces,  very  rough,  warty,  dark  maroon.  Seed  medium  to  small. 
Season,  February  to  April.     Guatemalan. 


Bul.  365] 


AVOCADO   CULTURE  IN   CALIFORNIA 


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62  UNIVERSITY  OF  CALIFORNIA EXPERIMENT  STATION 

F airhead. — Originated  on  place  of  G.  E.  Fairhead  at  Eagle  Rock, 
California,  in  1917.  Fruit  pyriform  to  broad  oval,  14  to  20  ounces, 
slightly  roughened,  mahogany-purple.  Seed  medium.  Season,  March 
and  April.    Guatemalan. 

Fuerie* — Description  given  above. 

Garcia. — Originated  on  place  of  M.  Garcia,  Duarte,  California,  in 
1921.  Fruit  pyriform,  15  ounces,  smooth,  green.  Seed  medium, 
sometimes  loose.     Season,  January  and  February.    Guatemalan. 

Kashlan. — A  Popenoe  introduction  from  Guatemala,  No.  10  (S. 
P.  I.  No.  43934).  Fruit  round  or  broadly  oval;  20  ounces,  smooth, 
green.     Seed  unusually  small.     Season,  May  and  June.     Guatemalan. 

Linda. — Introduced  from  Guatemala  by  E.  E.  Knight  of  Yorba 
Linda,  California,  as  No.  29  in  1914.  Fruit  round  to  elliptical,  large, 
32  to  36  ounces,  rough,  deep  purple.  Seed  medium.  Season,  May  to 
October.     Guatemalan. 

Lyon. — Originated  in  Hollywood,  California,  in  1908.  Fruit 
oblique  pyriform,  14  to  18  ounces,  rough,  dark  green.  Seed  large. 
Season,  April  to  July.  Tree  inclined  to  dwarfiness  due  to  overbearing. 
Guatemalan. 

Mayopan* — Introduced  by  Popenoe  from  Guatemala  as  No.  23 
(S.  P.  I.  No.  44680).  Fruit  nearly  round,  14  to  20  ounces,  slightly 
rough  to  corrugated,  purple.  Skin  very  thick.  Seed  small  to  medium. 
Season,  May  to  August.    Guatemalan. 

Ndbal* — Description  given  above. 

Northrop. — Originated  on  the  old  Northrop  place  near  Tustin, 
California,  about  1900.  Fruit  oblong-pyriform,  5  to  7  ounces,  smooth, 
purple.    Seed  medium.    October  and  November.    Mexican. 

Panchoy. — Introduced  by  Popenoe  as  No.  18  (S.  P.  I.  No.  44625) 
from  Guatemala.  Fruit  broadly  obovoid,  20  to  30  ounces,  rough, 
green.     Skin  thick ;  seed  small.    June  to  August.     Guatemalan. 

Premier. — Originated  on  place  of  A.  R.  Rideout  at  Whittier,  Cali- 
fornia. Fruit  round,  green,  15  to  20  ounces.  Season,  May  to  October. 
Guatemalan. 

Puebla* — Description  given  above. 

Queen.'* — Description  given  above. 

Stephens  Choice. — Sometimes  known  as  Choice.  Introduced  from 
Atlixco,  Mexico,  by  Wm.  Stephens  of  Montebello,  California.  Fruit 
slightly  pyriform  to  round,  16  to  20  ounces,  smooth,  green.  Seed 
medium  to  large.    Season,  June  to  August.     Guatemalan. 

Taft. — Description  given  above. 

Thompson* — Originated  on  place  of  Miss  Jessie  Thompson  at 
Montebello,  California,  in  1913.    Fruit  long-pyriform,  14  to  21  ounces, 


BUL.  365]  AVOCADO  CULTURE  IN  CALIFORNIA  63 

slightly  pebbled,  dark  purple.  Seed  very  small.  Season,  March  to 
June.     Guatemalan. 

Tiger. — Originated  at  Bishop  nursery,  Highland,  California. 
Fruit  pyriform,  10  to  16  ounces,  rough,  glossy,  purple.  Seed  medium. 
Season,  February  to  May.  Especially  adapted  to  interior  districts. 
Guatemalan. 

Tumin. — A  Popenoe  introduction  from  Guatemala,  No.  20  (S.  P.  I. 
No.  44627).  Fruit  spherical,  slightly  oblate,  18  to  24  ounces,  smooth, 
unusually  glossy,  purplish-black.  Seed  medium  to  small.  Fruit 
colors  several  months  before  ripening.  Season,  September.  Guate- 
malan. 

Worsham* — Originated  at  Whittier,  California,  in  1910.  Fruit 
oblique-oval,  12  to  14  ounces,  smooth,  green,  glossy.  Seed  medium  to 
large.  Tree  very  prolific.  Season,  December  to  February.  Thought 
to  be  a  Guatemalan-Mexican  hybrid. 


VARIETIES    MOST    HARDY    TO    COLD,    SUGGESTED    FOR    AMATEUR 

GROWERS 

Varieties  marked  with  an  asterisk  (*)  are  especially  recommended. 

Blake. — Originated  at  Pasadena,  California,  about  1903.  Fruit 
small,  slender-pyriform,  smooth,  light  green.  Seed  medium.  Season, 
October  and  December.    Mexican. 

Caliente. — Description  given  above. 

Dorothea, — Description  given  above. 

Duke* — Description  given  above. 

Fuerte* — Description  given  above. 

Northrop* — Description  given  above. 

Puebla* — Description  given  above. 

Snell. — Originated  at  Sierra  Madre,  California.  Fruit  slender- 
pyriform,  5  to  7  ounces,  green.  Season,  October  to  November.  Very 
high  in  fat  content.    Mexican. 

Topa-Topa, — Originated  on  old  Thatcher  place  at  Nordhoff,  Cali- 
fornia, in  1907.  Fruit  oblique  elongated-pyriform,  6  to  10  ounces, 
glossy,  purple.    Seed  medium.    September  to  December.    Mexican. 

More  detailed  information  concerning  these  and  the  numerous 
other  varieties  which  have  been  developed  is  available  in  the  annual 
reports  of  the  Variety  Committee  of  the  California  Avocado  Associ- 
ation which  are  published  in  the  yearbooks  of  the  Association,  the 
headquarters  of  which  are  maintained  at  1405  East  Eighth  Street, 
Los  Angeles. 


64  UNIVERSITY  OF  CALIFORNIA EXPERIMENT  STATION 

Fruits  of  all  promising  or  interesting  seedlings  or  introductions 
should  be  submitted  to  the  committee  for  classification,  study  and 
rating. 


UNITED  STATES  DEPARTMENT  OF  AGRICULTURE  INTRODUCTIONS 

The  assistance  of  the  United  States  Department  of  Agriculture  in 
introducing  promising  avocado  varieties  has  already  been  alluded  to. 
In  1917  about  twenty-three  superior  varieties  were  brought  in  from 
Guatemala,  representing  the  best  fruits  selected  by  Popenoe  in  his 
explorations  in  that  country  extending  over  a  period  of  several  years. 
Full  descriptions  and  illustrations  of  these  fruits  have  already 
appeared.12  They  have  now  been  under  test  and  observation  in  Cali- 
fornia sufficiently  long  to  have  attracted  widespread  interest.  A 
number  of  them  are  already  being  propagated  by  the  nurserymen. 
Several  of  these  varieties  are  especially  promising,  including  Nabal, 
Benik,  Cantel,  Kashlan,  Mayopan,  Panchoy  and  Tumin. 

More  recently  five  new  large-fruited  varieties  have  been  introduced 
from  the  Chota  Valley,  Ecuador,  following  explorations  by  Wilson 
Popenoe  in  1921. 13  Trees  of  each  of  these  varieties  are  now  under 
trial  in  southern  California.  They  give  promise  of  being  valuable 
additions  to  the  present  list  of  hardy  varieties. 

USES  OF  THE    FRUIT 

The  avocado  is  used  principally  as  a  salad  food.  As  its  general 
food  value  becomes  more  appreciated  it  will  undoubtedly  find  a  much 
larger  place  in  the  dietary  of  the  American  public.  A  discussion  of 
its  nutritive  value  is  given  in  Part  II  of  this  publication.  In  addition 
to  its  common  use  for  salads,  a  considerable  number  of  methods  of 
using  the  fruit  have  been  devised  by  housewives  and  chefs,  including 
avocado  ice  cream,  sandwich  filling  and  others.  The  reception  with 
which  these  innovations  have  been  met  is  indicative  of  the  popularity 
the  avocado  will  enjoy  once  it  is  placed  on  the  market  in  sufficient 
quantity  and  at  a  price  within  reach  of  all. 

The  demand  thus  far  has  readily  taken  care  of  all  the  fruits  pro- 
duced— good,   bad,   and   indifferent.     The   question   of   disposing   of 


12  Popenoe,  Wilson.  The  avocado  in  Guatemala.  U.  S.  Dept.  Agr.  Dept.  Bui. 
743:1-69.     1919. 

Popenoe,  Wilson.  Exploring  Guatemala  for  desirable  new  avocados.  Cali- 
fornia Avocado  Association  Annual  Eeport  1917:  104-138.     1918. 

!3  Popenoe,  Wilson.  Avocados  of  the  Chota  Valley,  Ecuador.  California 
Avocado  Association  Annual  Eeport  1922:  35-39.     1923. 


BUL.  365]  AVOCADO  CULTURE  IN  CALIFORNIA  65 

second  and  third  grade  fruit  has  not  become  at  all  pressing.  There 
may  come  a  time  in  the  future  when  some  other  outlet  will  have  to 
be  developed  for  these  grades.  Preliminary  experiments  with  a  view 
to  developing  possible  by-products  have  been  undertaken  both  by  the 
Agricultural  Experiment  Station,  University  of  California,  and  by 
the  Bureau  of  Chemistry  of  the  United  States  Department  of  Agri- 
culture. At  the  present  time  by  far  the  most  promising  products  are 
an  ice  cream  base  and  bases  for  the  preparation  of  cocktails  and  salads 
developed  by  the  Division  of  Fruit  Products  of  the  University  of 
California.  Experiments  on  canning  avocados  have  thus  far  failed  to 
develop  a  satisfactory  product.  Studies  looking  to  the  development 
of  methods  of  extracting  avocado  oil  and  possible  uses  for  the  product 
are  under  way  at  the  present  time. 

Recent  experiments  in  dehydration  of  the  avocado  by  Cruess  and 
Christie  have  indicated  that  a  satisfactory  product  can  be  produced 
that  will  return  to  a  satisfactory  fresh  condition  when  soaked  from 
five  to  six  hours  in  water.  Many  different  tests  were  conducted.  The 
most  satisfactory  results  were  obtained  from  the  following  procedure : 
The  fruit  is  halved  and  peeled.  It  is  then  cut  into  slices  a  quarter 
of  an  inch  or  less  in  thickness.  These  slices  are  placed  on  wooden 
trays  and  subjected  to  the  fumes  of  burning  sulfur  for  fifteen  minutes. 
They  are  then  dehydrated  to  a  bone  dry  consistency  through  the  use 
of  a  temperature  of  not  less  than  140°  Fahr.  and  not  more  than  180°. 
The  drying  ratio  is  between  5  and  6  to  1.  To  avoid  rancidification  of 
the  oil,  the  product  so  prepared  is  packed  in  vacuum  sealed  jars.  On 
soaking  in  slightly  salted  water  the  fruit  returns  to  its  original  size 
and  appearance  in  five  or  six  hours.  The  flavor  is  not  quite  as  rich 
nor  quite  as  pleasing  as  that  of  the  fresh  fruit.  However,  when  cut 
in  small  pieces  and  mixed  with  mayonnaise  dressing  it  makes  a  very 
pleasing  salad. 

YIELDS    AND    RETURNS 

The  wide  variation  in  yields  of  seedling  and  budded  trees  in  Cali- 
fornia makes  a  satisfactory  discussion  of  this  subject  difficult.  One 
point  is  certain,  namely,  that  the  practice  of  estimating  returns  on 
the  basis  of  the  large  crops  borne  by  old  seedling  trees  cannot  be  relied 
upon  with  any  measure  of  safety.  While  it  is  true  that  some  of  these 
of  both  Guatemalan  and  Mexican  types  have  produced  as  high  as  2500 
to  3000  fruits  in  a  single  season,  budded  trees  are  slower  in  growth 
and  so  far  have  not  shown  a  tendency  toward  bearing  abnormally  large 
crops.    There  has  not  been  sufficient  time  yet  for  trees  planted  under 


66  UNIVERSITY  OF  CALIFORNIA — EXPERIMENT  STATION 

orchard  conditions  to  demonstrate  the  kind  of  crops  they  will  con- 
sistently produce.  At  best,  conservative  estimates  alone  are  safe. 
From  observations  made  to  date  it  would  seem  that  a  mature  bearing 
orchard  tree  of  from  ten  to  fifteen  years  of  age  should  produce  a 
yearly  average  of  150  pounds  of  marketable  fruit. 

As  to  the  prices  which  growers  may  reasonably  expect  in  the 
future,  there  is  much  diversity  of  opinion.  The  food  value  of  the 
avocado  is  much  higher  than  that  of  any  other  fresh  fruit,  and  many 
growers  believe  this  fact  alone  will  be  sufficient  to  maintain  relatively 
high  price  levels.  On  the  other  hand,  it  appears  reasonable  to  con- 
clude that,  as  in  the  case  of  all  other  fruits,  price  levels  will  be  deter- 
mined entirely  by  the  relation  between  supply  and  demand.  These 
relations  have  been  such  in  recent  years  as  to  result  in  relatively  high 
prices.  As  to  whether  the  demand  can  be  increased  rapidly  enough  to 
maintain  present  price  levels  is  a  question  which  only  the  future  can 
answer.  It  seems  reasonable,  however,  to  believe  that  general  and 
fairly  pronounced  declines  in  price  levels  for  avocados  are  inevitable. 
In  any  event  it  is  certain  that  supplies  of  avocados  in  the  United 
States  will  increase  rapidly  for  some  years  to  come.  The  normal 
increase  in  production  in  California  alone  will  be  manyfold  in  the 
next  decade.  Some  of  the  leaders  in  the  industry  feel  that  before 
consumptive  demand  for  avocados  can  be  developed  to  the  point 
where  it  will  be  sufficient  to  utilize  all  of  the  avocados  California  can 
produce,  price  levels  must  drop  to  10  or  12  cents  per  pound.  It  is 
of  interest  in  this  connection  to  note  that  the  Florida  growers  have  in 
the  past  averaged  from  6  to  8  cents  per  pound  on  the  tree. 

Figures  covering  costs  of  production  are  not  available,  but  these 
are  probably  comparable  to  those  involved  in  citrus  fruit  production, 
the  usual  range  of  which  is  from  200  to  350  dollars  per  acre.  While 
at  present,  costs  of  insect  pest  and  disease  control  are  lower  than  with 
the  citrus  fruits,  in  all  probability  these  are  destined  to  increase  as 
insects  and  diseases  become  more  serious  and  wide  spread.  Moreover, 
costs  of  frost  and  wind  protection  will  probably  average  somewhat 
higher  than  for  the  citrus  fruits. 


BUL.  365]  AVOCADO  CULTURE  IN  CALIFORNIA  67 


OUTLOOK— PRESENT  AND    FUTURE 

That  the  avocado  has  come  to  stay  as  an  important  crop  in  Cali- 
fornia is  assured  beyond  a  doubt.  With  the  ever  increasing  land 
values,  especially  in  the  more  climatically  favored  portions  of  the 
state,  crops  yielding  high  gross  returns  per  acre  must  be  grown.  As 
population  becomes  more  and  more  dense  the  tonnage  of  food  produced 
per  acre  must  likewise  increase ;  the  food  value  of  the  fruit  and  its 
potentially  high  production  per  acre  are  sufficient  reasons  to  justify 
its  place  in  California  agriculture. 

Regardless  of  its  promising  future,  however,  certain  conditions 
surrounding  the  growing  industry  should  be  clearly  recognized.  Avo- 
cado growing  is  a  new  industry  and  is  far  from  being  either  standard- 
ized or  stable.  The  initial  investment  in  land  and  in  nursery  trees 
required  is  high,  the  risks  are  perhaps  greater  than  with  the  well 
established  fruit  industries.  The  costs  of  production  are  not  low; 
the  avocado  is  a  tender  crop  and  requires  unusual  care ;  frost  protec- 
tion must  be  almost  universally  provided  if  investments  are  to  be 
protected.  Adequate  capital  must  be  available  to  carry  the  grower 
through  until  the  trees  arrive  at  a  productive  bearing  age  and  to 
provide  sufficient  care  without  fail  all  during  this  initial  period. 

At  the  present  stage  of  development  avocado  growing  is  not  an 
industry  for  the  inexperienced  person  of  limited  means.  The  efforts 
being  made  by  some  individuals  and  companies  in  California  and 
Florida  to  attract  the  small  investor  with  the  hope  of  large  returns, 
based  on  the  behavior  of  exceptional  trees  and  abnormal  prices,  cannot 
be  too  strongly  condemned.  The  industry  cannot  develop  with  safety 
on  such  a  basis. 

Before  the  industry  can  become  stabilized,  much  investigational 
work  will  be  required.  Hardy  varieties  which  consistently  produce 
good  crops  of  high  quality  fruit  are  yet  to  be  developed.  The  avocado 
districts  of  the  world  have  been  combed  for  varieties  most  suited  to 
California  conditions,  and  material  is  here  from  which  to  develop  these 
varieties.    Much  progress  has  already  been  made  in  that  direction. 

So  far  no  attempts  have  been  made  to  improve  the  avocado  by 
breeding.  The  value  of  the  fruit  as  a  food  product  lies  in  its  high  oil, 
mineral,  and  protein  content.  At  present  the  oil  content  varies  from 
9%  to  32%  and  the  protein  content  from  1.3%  to  4.6%  ;  obviously 
from  a  nutritional  point  of  view  the  best  varieties  should  have  a 
maximum  content  of  oil  and  protein  provided  flavor  and  quality  are 


68  UNIVERSITY  OF  CALIFORNIA EXPERIMENT  STATION 

also  maintained.  The  development  of  the  fruit  in  this  direction  lies 
largely  in  the  hands  of  the  plant  breeder.  The  effect  of  environmental 
conditions  on  the  quality  and  composition  of  the  fruit,  however,  must 
not  be  lost  sight  of  and  a  thorough  study  of  the  influence  of  such 
factors  still  remains  to  be  made. 

The  behavior  of  chance  seedlings  scattered  through  northern  and 
central  California  indicates  the  possibilities  of  the  development  of 
hardy  varieties  suited  to  the  climatic  conditions  of  those  sections.  The 
future  will  undoubtedly  witness  breeding  and  selection  investigations 
with  a  view  to  greatly  expanding  the  area  in  which  this  valuable  fruit 
can  be  grown.  Many  sections  in  southern  California  also  await  the 
development  of  hardier  varieties  than  those  now  available. 

The  area  in  the  United  States  in  which  the  present  varieties  of 
avocados  can  be  successfully  grown  is  decidedly  limited,  occurring 
only  in  certain  especially  favored  sections  of  California  and  Florida. 
On  account  of  dangerous  insect  pests  avocados  cannot  be  shipped  into 
the  United  States  from  the  American  tropics,  with  a  few  exceptions 
only,  mainly  Cuba. 

On  the  other  hand,  it  should  be  remembered,  however,  that  the 
avocado  acreage  in  Florida  and  California,  while  relatively  small,  can 
still  be  very  greatly  expanded,  and  that  the  possibilities  in  Cuba  are 
even  greater  than  in  the  two  states  combined. 

It  is  certain  that  ever  increasing,  intensive  competition  faces  the 
California  avocado  grower.  Present  price  levels  will  in  all  probability 
decline,  and  the  maintenance  of  relatively  high  price  levels  will 
eventually  advance  land  values  to  the  point  where  the  interest  on  the 
investment  will  materially  reduce  the  net  returns. 

Like  all  other  young  horticultural  industries,  avocado  production 
may  be  expected  to  have  its  ups  and  downs  before  it  is  eventually 
stabilized  on  a  moderately  profitable  basis.  There  is  much  reason  for 
believing  that  within  the  next  decade  the  industry  will  have  passed 
through  the  exploitation  stage  and  settled  down  to  a  commercial  basis 
when  the  profits  will  not  be  materially  different  from  those  of  other 
California  specialty  subtropical  fruits  such  as  the  orange,  lemon, 
grapefruit  or  date. 

In  any  event,  the  future  success  of  the  industry  depends  on  the 
employment  by  the  growers  of  the  same  methods  which  have  brought 
success  to  the  growers  of  other  California  fruit  crops,  namely  the 
production  of  the  best  possible  quality  fruit,  the  preparation  of  it  for 
market  in  the  most  attractive  manner,  rigid  adherence  to  grading  and 
standardization,  and  the  use  of  the  most  efficient  merchandizing 
methods. 


BUL.  365]  AVOCADO  CULTURE  IN   CALIFORNIA  69 


ACKNOWLEDGMENTS 

The  author  wishes  to  express  his  appreciation  to  F.  0.  Popenoe 
of  Altadena,  Wm.  Hertrich  of  El  Moleno,  Dr.  J.  Eliot  Coit  of  Pasa- 
dena, and  other  members  of  the  California  Avocado  Association  for 
helpful  suggestions  and  criticisms  in  connection  with  the  preparation 
of  the  manuscript  for  the  first  edition  of  this  bulletin. 

He  is  especially  indebted  to  Professor  Robert  W.  Hodgson  of  the 
Division  of  Subtropical  Horticulture  of  the  College  of  Agriculture  for 
assistance  in  the  preparation  of  the  original  bulletin  and  for  its 
revision  and  expansion  into  the  present  publication.  In  this  revision 
valuable  suggestions  were  received  from  Geo.  B.  Hodgkin,  Secretary- 
Manager  of  the  Calavo  Growers  of  California,  Mrs.  Adeltha  Peterson, 
Secretary  to  Mr.  Hodgkin;  E.  C.  Dutton  of  Anaheim,  President  of 
the  California  Avocado  Association,  and  Dr.  J.  Eliot  Coit,  Chairman 
of  the  Association  Committee  on  Varieties,  for  which  grateful 
acknowledgment  is  hereby  made. 


70  UNIVERSITY  OF  CALIFORNIA EXPERIMENT  STATION 


THE  NUTRITIVE  VALUE  OF  THE  AVOCADO 
Part  II 

M.  E.  JAFFA  and  H.  GOSS 


The  investigation14  here  reported  includes  110  analyses  represent- 
ing 68  different  varieties  of  the  avocado.  These  data  emphasize  the 
value  of  this  fruit  as  an  excellent  source  of  easily  digested  vege- 
table fat. 

THE   AVERAGE   COMPOSITION    OF    FRESH    FRUITS 

A  reference  to  the  composition  of  fresh  fruit  in  general  shows 
that  the  amount  of  water  is  large,  averaging  about  83  per  cent,  and 
that  the  percentage  of  the  nutrients  indicates  that  the  main  food  value 
is  derived  from  carbohydrates.  In  nearly  all  cases  sugars  predominate, 
starch  being  present  in  small  amounts  only. 

The  protein  content  of  fruits  is  low,  averaging  for  the  loquat  about 
0.2  of  one  per  cent ;  apples  and  pears,  0.4-0.5  per  cent ;  fresh  prunes, 
0.9  per  cent;  melons,  0.5  per  cent;  berries,  1-1.3  per  cent;  oranges, 
0.8-1.0  per  cent;  grapes  and  bananas,  1.2-1.5  per  cent.  The  average, 
therefore,  for  protein  for  the  fresh  fruits  enumerated  is  practically 
0.72  per  cent.    The  olive  contains  approximately  2.5  per  cent  protein. 

The  per  cents  for  the  mineral  matter  or  ash  in  fresh  fruits  are  as 
follows :  apples  and  pears,  0.3-0.4 ;  grapes,  0.5 ;  figs,  0.6 ;  berries,  0.6 ; 
oranges,  0.5  ;  melons,  0.5  ;  fresh  prunes,  0.6 ;  bananas,  1.0.  The  average 
being  0.55  per  cent,  while  the  correspnding  figure  for  meat  is  about 
1  per  cent. 

It  must  not  be  forgotten,  however,  that  while  the  amount  of  ash  is 
small,  the  percentage  of  potassium  in  the  ash  is  high.  This  is  a  very 
valuable  base-forming  element  which  is  necessary  in  the  maintenance 
of  the  normal  neutrality  of  the  blood  and  tissues.  The  importance 
of  the  mineral  matter  in  nutrition  and  the  necessity  of  carefully 
selecting  the  dietary  so  as  to  secure  a  proper  balance  between  the 
base-forming  and  acid-forming  elements  is  becoming  more  and  more 
apparent. 


!4  Credit  is  due  to  Miss  Mattie  E.  Stover  and  F.  W.  Albro  for  assistance  in 
chemical  work  incidental  to  this  investigation. 


BUL.  365]  AVOCADO  CULTURE  IN  CALIFORNIA  71 

Fat  is  present  in  very  small  proportions  in  fresh  fruits.  This 
constituent  is  generally  reported  as  "ether  extract"  which  often  con- 
tains other  materials  than  the  true  fats  or  oil,  such  as  coloring  matter, 
wax  found  in  the  skin,  etc.  The  figure  reported  for  fat  in  most  fruits, 
therefore,  is  seldom  a  true  indication  of  the  content  of  this  nutrient. 

Fruits  are  important  sources  of  water-soluble  vitamins.  Particu- 
larly is  this  true  of  the  citrus  fruits  which  are  rich  in  vitamin  C.  The 
deciduous  fruits  shown  appreciable  percentages  of  B  and  berries,  like 
raspberries  and  strawberries,  show  also  a  high  content  of  vitamin  C. 

Mature  California  grown  fruits  only  are  included  in  above  tabu- 
lation. 

COMPOSITION  OF  THE  AVOCADO 

A  survey  of  the  data  presented  in  the  accompanying  tables  shows 
the  avocado  to  differ  widely  in  many  respects  from  the  average  for 
fresh  fruits  and  proves  it  worthy  of  special  consideration.  It  might 
well  be  said  to  be  in  a  class  by  itself. 

The  tables  are  replete  with  interesting  points,  all  very  favorable 
to  the  avocado.  The  total  dry  matter  in  the  edible  portion  is,  in 
nearly  every  instance,  greater  than  that  noted  for  any  other  fresh 
fruit.  The  average  for  the  avocado,  based  on  examination  of  mature 
California  fruits  is  29.44  per  cent.  The  nearest  approach  to  this 
figure  is  found  in  the  banana  with  about  25  per  cent  dry  matter.  It 
must  be  remembered,  however,  that  while  there  may  not  be  so  much 
difference  in  the  total  amount  of  solids  of  the  two  fruits  in  question, 
there  is  a  great  difference  in  the  nature  of  the  nutrients.  Sugar  and 
starch  predominate  in  the  banana  as  against  fat  in  the  avocado. 

It  has  been  stated  that  the  protein  per  cent  in  all  fruits  is  low, 
averaging  less  than  one  per  cent.  It  will  be  seen  from  the  table  that 
the  minimum  figure  for  protein  in  the  avocado  is  1.14,  which  is  about 
75  per  cent  of  the  maximum,  1.5  per  cent,  noted  for  figs  and  currants. 
The  maximum,  4.39  per  cent,  credited  to  Bartley  avocado  grown  at 
Santa  Ana,  corresponds  to  the  protein  content  of  some  dried  fruits. 

It  is  of  interest  in  passing  to  note  that  a  sample  of  the  Lyon  variety 
analyzed  by  the  U.  S.  Department  of  Agriculture  also  shows  the  same 
figure,  4.39  per  cent,  as  the  maximum  for  the  protein  for  this  variety. 

In  seven  of  the  varieties  the  protein  is  in  excess  of  3  per  cent ;  in 
36  varieties  between  2  and  3  per  cent ;  while  the  average  for  83  mature 
varieties  is  2.10  per  cent. 

It  therefore  may  be  said  that  so  far  as  protein  in  fresh  fruits  is 
concerned,  the  avocado  stands  in  the  lead. 


72 


UNIVERSITY  OF  CALIFORNIA EXPERIMENT  STATION 


TABLE  1. — Showing  the  Composition  of  the  Avocado 


Variety 

Locality 

Weight 

of 

fruit 

grams 

Refuse 
per  cent 

Edible  portion 

Water 
per  cent 

Carbo- 
Protein      Fat     hydrates     Ash 
per  cent  per  cent  per  cent  per  cent 

1. 

Azusa 

Azusa 

....       198 

28.30 

67.05 

1.94 

21.06 

8.59 

1.36 

2. 

Azusa 

Azusa 

....      169 

13.60 

62.69 

2.91 

26.44 

6.15 

1.81 

Average  Azusa 

....      184 

21.00 

64.87 

2.43 

23.75 

7.37 

1.58 

3. 

Bartley 

Santa  Ana 

....      928 

21.33 

77.12 

4.39 

13.35 

3.74 

1.40 

4. 

Beauty 

Orange 

....      426 

34.07 

72.68 

2.48 

15.26 

8.22 

1.36 

5. 

Benik 

Duarte 

....      518 

31.06 

69.98 

1.97 

22.02 

4.42 

1.61 

6. 

Blake 

Pasadena 

....       150 

32.66 

65.76 

1.88 

25  50 

5.52 

1  34 

7. 

Blake 

Whittier 

....       120 

31.60 

68.24 

1.81 

21.65 

8.18 

1.12 

8. 

Blakeman 

Altadena 

....      472 

30.30 

74.33 

2.61 

17.27 

4.94 

0.85 

9. 

Blakeman 

Altadena 

....      454 

20.81 

77.72 

3.15 

15.43 

2.59 

1  11 

463 

25.57 

76.87 

2.88 

16.35 

3.76 

0.98 

10. 

Brodia 

Orange 

...      405 

36.80 

80.80 

1  26 

10.88 

6.30 

0.76 

11. 

Cabnal 

Duarte 

....      459 

33.11 

67.15 

2.08 

23.71 

5.69 

1.37 

i  a 

Cantel 

Cardinal 

351 

24.79 
19.00 

72.04 
79.66 

2.43 
2.56 

19.00 
10.70 

4.90 
6.48 

1.59 

13. 

Florida 

:...      587 

0.60 

14. 

Caribou 

Duarte 

....      464 

31.04 

82.31 

1.34 

10.33 

4  60 

1.42 

15. 

Caribou 

Duarte 

....      486 

19.80 

79.02 

2.21 

12.00 

5.43 

1.34 

Average  Caribou 

....      475 

25.42 

80.66 

1.77 

11.17 

5.02 

1.38 

16. 

Carmen 

Altadena 

....       139 

31.30 

63.39 

1  22 

26.38 

7.46 

1.55 

17. 

Carton 

San  Fernando 

....       169 

41.20 

70.43 

2.60 

19.50 

6.29 

1.18 

18. 

Carton* 

Riverside 

....       108 

26.06 

78.32 

1.38 

12.71 

6.60 

0.99 

19. 

Challenge*. ... 

Hollywood 

....     1060 

40.57 

79.61 

3.43 

13.14 

2.62 

1.20 

20 

Challenge 

Hollywood 

....      669 

17.78 

76.23 

2.81 

16.37 

3.05 

1.54 

21. 

Champion 

Orange 

...      506 

30.00 

74.32 

2.59 

16.54 

5.31 

1.24 

22. 

Chappelow. ... 

Monrovia 

....      181 

22.43 

60.94 

1  40 

29.10 

6  85 

1.71 

23. 

Chappelow 

Monrovia 

....       173 

31.00 

63.58 

2  63 

24.43 

8.06 

1.30 

24. 

Chappelow 

Monrovia 

....       104 

36.34 

63.74 

2.19 

22.81 

10.00 

1.26 

25. 

Chappelow... 

Monrovia 

....     no 

36.90 

58.99 

2.79 

27.66 

9.33 

1.23 

26. 

Chappelow 

Monrovia 

...       159 

23.30 

70.77 

2.25 

20.28 

5.13 

1.57 

Average 

Chappelow 

....       145 

29.99 

63.61 

2.25 

24.85 

7.88 

1.41 

27. 

Chappelow*.. 

Altadena 

80 

30.30 

75.34 

2.30 

14.66 

6  80 

0.90 

28. 

Condon 

Pasadena 

....       143 

34.20 

69.11 

2.50 

21.00 

6.73 

0.66 

29. 

Condon 

Pasadena 

....       150 

24.00 

70.30 

1.31 

23  55 

3.62 

1.22 

Average  Condon 

....       146 

29.10 

69.70 

1.91 

22.28 

5.17 

0.94 

30. 

Dickey 

Hollywood 

....      363 

30.00 

60.50 

2.20 

27.11 

8.76 

1.43 

31. 

Dickey* 

Nordhoff 

....      560 

24.55 

81.10 

2  01 

11.81 

3.75 

1.33 

32. 

Dickinson 

Puente 

....      254 

29.99 

72.04 

1.56 

20.36 

4.69 

1.35 

33. 

Fowler 

Pasadena 

132 

35.80 

70.33 

1.60 

21.20 

5.61 

1.26 

34 

Fuerte 

Fuerte 

Average 

....      315 

25.71 
26.14 
25.92 

66.30 
68.32 
67.31 

1.42 
1.36 
1.39 

25.32 
24.23 
24.77 

5.68 
4.82 
5.25 

1.28 

35 

566 

1  27 

Fuerte 

440 

1.28 

36 

Fuerte* 

Fuerte 

.  ..      254 

23.62 
26.48 

80.88 
65.26 

1.04 
1.40 

11.61 
28.68 

5.53 
3.22 

0.94 

37. 

Altadena 

270 

1.44 

38. 

Fuerte 

Altadena 

256 

28.71 

65.67 

1.51 

26.60 

4.62 

1.60 

Average  Fuerte 

263 

27.59 

65.46 

1.46 

27.61 

3.92 

1.52 

39. 

Ganter 

Whittier 

205 

16.60 

63.86 

2.25 

25.60 

6.58 

1.71 

40 

Ganter* 

Harman* 

Whittier 

197 

26.80 
35.50 

77.87 
75.17 

2.13 
1.69 

16.48 
15.25 

2.48 
7.00 

1.04 

41. 

Sherman 

127 

0.89 

42. 

Harman* 

Sherman 

136 

37.90 

76.09 

1.24 

15.34 

6.65 

0.68 

43. 

Harman* 

Sherman 

170 

37.40 

75.42 

1.47 

16.26 

5.86 

0.99 

Average  Harman* 

144 

36.93 

75.56 

1.47 

15.62 

6.50 

0.85 

44. 

Harman 

Sherman 

235 

46.38 

71.58 

2.50 

19.33 

5.32 

1  27 

45. 

Harman 

Sherman 

263 

34.70 

74.70 

1  60 

18.30 

4.60 

0  80 

46. 

Harman 

Sherman 

233 

33.50 

72.05 

1.43 

21.51 

4.24 

0  77 

47. 

Harman 

Sherman 

215 

34.90 

73.44 

1.14 

18.68 

5.17 

1.57 

48. 

Harman 

Sherman 

192 

28.00 

72.75 

1.16 

19.18 

5.86 

1.05 

Average  Harman  mature 

227 

41.61 

72.90 

1.57 

19.40 

5.03 

1.10 

*  Immature. 

BuL.  365]  AVOCADO  CULTURE  IN   CALIFORNIA  73 

TABLE  1.— (Continued) 

Edible  portion 
Weight 


of  Carbo- 

fruit  Refuse  Water  Protein  Fat  hydrates     Ash 

Variety                       Locality                 grams  per  cent  per  cent  per  cent  per  cent  per  cent  per  cent 

49.  I.  X.  L.* Duarte 705  31.60  84.27  2.12  7  50  4.70  1.41 

50.  IX.  L Duarte 800  23  00  78.12  2  17  13.47  4.74  1.50 

51.  Kist Yorba  Linda 456  31.35  76.84  1.51  12.16  8.13  1  36 

52.  Kist Yorba  Linda 478  28  20  74.71  2  41  14.92  6  49  1.47 

Average  Kist 467  29.77  75.78  1.96  13.54  7.31  1.41 

53.  Lamat Duarte 332  30.42  77.32  1.42  14.29  5.57  1  40 

54.  Lambert Hollywood 285  33.40  76.52  2.86  14.31  5.40  0.91 

55.  Lyon Hollywood 453        75.78  2.48  16.31  4.38  1.05 

56.  Lyon La  Habra 453  26  50  74.80  2.76  15.58  6  01  0  85 

57.  Mattern Unknown 92  44.00  61.55  2.20  25.70  8.94  1.61 

58.  Mayapan Duarte 397  37.28  68.33  1.77  22.83  5.59  1.48 

59.  Mayapan Duarte 449  28.06  70.26  2.25  21.80  4.13  1.56 

Average  Mayapan 423  32.67  69.29  2.01  22.32  2.86  1.52 

60.  Meserve Puente 331  40  00  74  66  2.19  17.01  4  78  1.36 

61.  Miller Hollywood 184  35.80  66.60  3.70  23.70  4  51  1.49 

62.  Miller Pasadena 275  40.00  63.68  3.36  27.45  4.18  1.33 

63.  Monrovia Altadena 166  37.00  64.18  2.09  25.34  6.73  1  66 

64.  Nimlich Duarte 860  24.42  78.55  1.53  13.93  4.83  1.16 

65.  Northrop Santa  Ana 164  34.70  66.31  2.36  23.00  7.12  1  21 

66.  Pankay Duarte 385  41.30  73.15  1.58  14.56  9.10  1.61 

67.  Pankay Duarte 310  46.12  71.03  1.64  16.30  9.61  1.42 

Average  Pankay 347  43.76  72.09  1.61  15.43  9.36  1.51 

68.  Pomona Sacramento 79  43.00  61.84  3  50  25.36  7.36  1.94 

69.  Popenoe  101 Altadena 327  23.82  58.71  2.39  3159  5.65  1.66 

70.  Popenoe  101 Altadena 375  29.34  60  78  1.82  29.78  5  92  1.70 

Average  Popenoe  101 346  26.58  59.74  1.65  30.68  5.78  168 

71.  Puebla* Altadena 168  34  00  80 .59  1.76  11.32  5  22  1.11 

72'   Puebla Altadena 280  27.50  69.47  1.66  20.94  6  65  1.28 

73.  Puebla Altadena 158  36  00  67  53  1.83  26.14  3.16  1.34 

Average  Puebla  mature 219  31.75  68.50  1.74  23.54  4.91  1.31 

74.  Purdy Whittier 168  32.10  60.28  1.14  31.60  5.49  1.49 

75.  Purple  Prolific Orange 219  45.90  69.30  1.67  19.93  8.27  0.83 

76.  Queen Unknown 663  29.15  73 .80  2  21  16.35  6.01  1.63 

77.  Queretaro Yorba  Linda 217  37.80  71.46  2  85  17.45  6.79  1.45 

78.  Queretaro Altadena 164  36.60  71.46  2  34  18.21  6.56  1.43 

79.  Rhoad Orange 395  37.00  82.46  1.19  9.78  6.03  0.54 

80.  Rita* Orange 321  42.68  71  05  1.57  14.13  12.25  1.00 

81.  Royal Hollywood 600  26  33  76.34  1.39  15.61  5.97  0.69 

82.  Royal  Purple San  Diego 200  26.00  72.96  1.72  19.39  4.84  1.09 

83.  Senor Orange 528  21.00  74.70        1.69  17  03  5.45  1.13 

84.  Sharpless* Santa  Ana 471  21.23  76.73  2.15  15.73  3.69  1.70 

85.  Sharpless* Santa  Ana 555  22.50  75.33  3.06  15.87  4.52  1.22 

Average  Sharpless* 513  2186  76  03  2.60  15.80  4.11  1.16 

86.  Sharpless Santa  Ana 594  23  10  71.21        1.70  20  54  5.43  1.12 

87.  Sharpless Santa  Ana 536  24.10  72.63        1  27  18.77  6.39  0.94 

Average  Sharpless 565  23.65  71.92        1.48  19.65  5.91  1.03 

88.  Sinaloa Whittier 616  23.40  73.55  2.67  16.43  5.57  1.78 

89.  Spinks Duarte 388  31.50  76.22        1.50  14.83  5.96  1.49 

90.  Spinks Duarte 877  20.30  75.72  2.10  16.01  4.74  1.43 

Average  Spinks 633  25.90  75.97        1.80  15.42  5.35  146 

91.  Surprise Hollywood 538  26.00  82.51        1.90  9.96  4.86  0.77 

92.  Taft Orange 626  29.00  72.53        2.66  18.54  5.16  1.11 

93.  Taft* Orange 417  25.00  76.11        2.30  14.67  6.00  0.92 

94.  Taft* Orange 296  27.00  77.25        3.44  12.59  4.91  1.81 

fet               Average  Taft* 356  26.00  76.68        2.87  13.63  5.45  1.37 

95.  Oopa-Topa Nordhoff 123  27.70  75.00        2.30  15.48  6.14  1.08 

96.  Trapp Florida 638  28.50  78.66        1.61  9.80  9.08  0.85 

*  Immature. 


74  UNIVERSITY  OF  CALIFORNIA EXPERIMENT  STATION 

TABLE  1.— (Continued) 

Edible  portion 
Weight 


of  Carbo- 

fruit     Refuse  Water  Protein  Fat  hydrates  Ash 

Variety  Locality  grams  per  cent  per  cent  per  cent  per  cent  per  cent  per  cent 

97.  Ultimate Orange 277        37.40  75.01        1.57  14.51  4.88  1.03 

98.  Walker Sherman 174        37.10  68.66        3.15  18.71  7.55  1  93 

99.  Wagner Hollywood 259        47.00  74.84        2.77  16.03  5.05  1.30 

100.  Dr.  Weldon Duarte 450        41.00  63.75        2.57  24.29  7.79  1.60 

101.  W.  I.  G Altadena 123        28.50  60.00        2.63  26.73  9.08  1.56 

102.  White Santa  Barbara 162        35.00  77.06        1.74  14.64  5.49  1.07 

Weight 

of  Carbo- 

No.  of      fruit     Refuse  Water  Protein  Fat  hydrates     Ash 

analyses  grams  per  cent  per  cent  per  cent  per  cent  per  cent  per  cent 

Maximum 83            928        47.00  82.31        4.39  31.60  10.00  1.94 

Minimum 83              79        13.60  58.71        1.14  9.78  2.59  0.54 

Average 83            347        32.11  70.56        2.10  20.06  5.95  1.32 

Mature  California  grown  fruits  only  are  included  in  above  tabulation. 


Partial  Analyses 


Variety  Locality 

1.  Atlixco Yorba  Linda 

2.  Atlixco Yorba  Linda 

Average  Atlixco 

3.  Goldie San  Diego 

4.  Knight Yorba  Linda 

5.  Linda Unknown 

6.  Snell Sierra  Madre 

7.  Tahiti San  Diego 

8.  Whittier Whittier 


Weight 
of  fruit 
grams 

Refuse 
per  cent 

Water 
per  cent 

Fat 
per  cent 

352 

26.52 

63.70 

28.80 

532 

26.86 

63.10 

26.90 

442 

26.69 

63.40 

27.95 

165 

35.50 

56  50 

26.67 

570 

26.95 

71.03 

23.31 

890 

20.23 

82.66 

7.48 

306 

29.00 

55.00 

32.70 

256 

19.50 

50.60 

23.20 

687 

23.00 

75.20 

21.20 

The  carbohydrate  content  of  the  avocado  is  low  as  compared  with 
this  constituent  in  fresh  fruits.  The  average  for  the  83  mature 
varieties  is  5.95  per  cent,  with  a  maximum  of  10  per  cent  and  a  mini- 
mum of  2.59  per  cent. 

The  figures  quoted  in  the  table  for  carbohydrates  include  crude 
fiber  which  was  not  determined  in  every  case.  Analyses  of  a  number 
of  samples  have  shown,  however,  that  this  ingredient  would  average 
about  1.5  per  cent,  which  compares  very  favorably  with  the  content 
of  crude  fiber  in  other  fresh  fruits. 

It  is  of  decided  interest  to  note  that  the  percentage  of  mineral 
matter  in  the  avocado  is  much  higher  than  that  recorded  for  any  other 
fresh  fruit.  The  minimum  0.54  per  cent,  reported  for  the  Rhoad 
variety,  equals  approximately  the  average  for  most  of  our  fresh  fruits, 
while  the  average  for  the  avocado,  1.32  per  cent,  shows  that  it  contains 
twice  as  much  mineral  matter  as  that  yielded  by  any  other  fruit. 

The  following  analysis  of  the  ash  of  the  avocado  shows  that,  like 
other  fruit,  the  avocado  yields  an  excess  of  the  base-forming  elements : 


BUL.  365]  AVOCADO  CULTURE  IN  CALIFORNIA  75 

Silica   0.50 

Phosphoric  acid  17.40 

Lime    4.72 

Magnesia    5.30 

Iron   1.51 

Aluminum  2.58 

Manganese    Trace 

Sulfuric   acid   11.24 

Chlorin    14.36 

Potash  26.23 

Soda  18.55 

101.89 
Oxygen  equivalent  to  chlorin  2.09 

99.80 

Nearly  one-half  of  the  ash  consists  of  soda  and  potash,  the  latter 
predominating.  Magnesia  and  lime  occur  in  comparatively  small 
amounts,  about  5  per  cent  each ;  the  phosphoric  acid  averaging  about 

17.5  per  cent,  with  1.5  per  cent  of  iron. 

The  foregoing  discussion  clearly  indicates  that  so  far  as  protein 
and  ash  in  fresh  fruits  are  concerned,  the  avocado  stands  at  the  head 
of  the  list,  and  with  reference  to  the  carbohydrates,  contains  on  an 
average  fully  50  per  cent  of  that  found  in  many  fresh  fruits.  These 
facts  alone  would  warrant  due  consideration  of  the  value  of  the 
avocado  as  a  fresh  fruit. 

The  chief  value  of  the  avocado  as  food,  however,  is  due  to  its  high 
content  of  fat.  This  varies,  as  shown  by  the  analyses,  from  a  minimum 
of  9.78  per  cent  to  a  maximum  of  31.6  per  cent,  with  an  average  of 

20.6  per  cent. 

Reviewing  the  analytical  data,  it  will  be  seen  that  15  varieties 
show  more  than  25  per  cent  fat  and  14  other  varieties  an  excess  of 
20  per  cent.  The  only  fruit  comparable  with  the  avocado  in  this 
respect  is  the  olive.  In  this  connection,  it  is  of  interest  to  note  the 
comparison  as  shown  in  the  following  table,  of  the  fat  percentages  of 
the  edible  portion  of  ten  varieties  of  the  avocado  containing  25  per 
cent  or  more  of  fat,  with  ten  varieties  of  the  olive. 

The  figures  in  table  2  indicate  that  the  avocado  ranks  higher  in 
fat  or  oil  than  the  average  or  commonly  used  olive.  The  olive  also 
has  the  disadvantage  of  requiring  special  treatment  before  it  is  ready 
for  consumption  and  should  really  rank  as  a  processed  fruit  rather 
than  a  fresh  one.  The  data  in  the  table  show  that,  when  considering 
the  dry  matter  only,  the  Purdy  has  the  highest  percentage  of  fat.  In 
the  original  condition,  the  Blake  and  the  Chappelow  differ  in  fat  by 


76 


UNIVERSITY  OF  CALIFORNIA EXPERIMENT  STATION 


nearly  4  per  cent,  which  difference  is  practically  eliminated  when  com- 
parison is  made  on  a  water-free  basis,  which  is  the  only  true  way  to 
compare  the  nutritive  value  of  fruits. 


TABLE  2. — Showing  Percentage,  of  Fat  or  Oil  in  the  Avocado  and  Olive 

Olive— Edible  Portion 

Original  material 

Per  ct. 

Variety  oil 

Corregiolo 27.68 

Nigerina 26.16 

Nevadillo  Blanco 22.92 

Mission 22.51 

Rubra 22.01 

Pendulina 21.36 

Redding  Picholine  20.83 

Macrocarpa 20.41 

Manzanillo 19.73 

Columbella 19.54 


Avocado— Edible  Portion 

Original  material 

Water-fr 

Per  ct.         Per  ct. 

Per  ct. 

Variety 

water             fat 

fat 

Purdy 

60.28           31.60 

79.70 

Popenoe 

59.74           30.68 

76.20 

Chappelow 

60.94            29.10 

74.40 

Fuerte 

65.26           28.68 

82.50 

Miller 

63.68            27.45 

75.60 

Dickey 

60.50            27.11 

68.70 

Azusa 

62.69            26.44 

70.90 

Carmen 

63.39            26.38 

72.10 

Ganter 

63.86            25.60 

70.80 

Blake 

65.76            25.50 

74.50 

CALORIC  VALUE 

While  it  is  true  that  the  real  value  of  any  food  is  not  always  rep- 
resented by  the  heat  units  or  calories,  at  the  same  time,  the  total  food 
value  is  so  indicated.  This  difference  between  the  real  food  value 
and  the  total  food  value  is  not  always  properly  understood.  For 
instance,  the  energy  value  of  a  pound  of  sugar  is  1820  calories,  while 
the  corresponding  value  for  lean  meat  is  less  than  1000  calories.  Yet 
Ave  would  hardly  say  that  the  real  value  of  a  pound  of  sugar  was  1.8 
times  that  of  a  pound  of  lean  meat,  if  the  question  of  growth  were 
under  consideration.  When,  however,  the  matter  of  energy  is  being 
discussed  the  case  is  entirely  different,  and  the  value  of  a  food  as  a 
source  of  energy  varies  directly  with  its  caloric  value. 

The  energy  values  of  the  edible  portion  of  the  commonly  used  fresh 
fruits  are  low,  ranging  from  a  minimum  of  175  calories  to  a  possible 
maximum  of  400  calories  per  pound. 

TABLE  3. — Showing  the  Energy  Value  of  the  Avocado 

Energy  value 
per  pound 
Variety  calories 

Mayapan 992 

Miller 1,159 

Northrop 1,101 

Pomona 1,223 

Popenoe 1,376 

Puebla 1,026 

Queen 812 

Sharpless 928 

Sinaloa 814 


Variety 

Energy  value 

per  pound 

calories 

1,235 

Blake 

1  083 

Blakeman 

783 

1,100 

Chappelow 

1,184 

1,293 

Dickinson 

958 

Fuerte 

1,187 

Ganter 

1,195 

Harman 

904 

Lyon 

785 

Average,, 


1,056 


BUL.  365]  AVOCADO  CULTURE  IN  CALIFORNIA  77 

An  inspection  of  table  3  shows  that  the  avocado  has  a  far  higher 
value  in  this  respect,  the  average  for  twenty  varieties,  being  1056  per 
pound,  or  more  than  twice  the  maximum  (400  calories)  noted  for 
other  fresh  fruits.  The  minimum,  783  calories,  approaches  very  closely 
to  this  figure.  The  maximum,  1376  calories  per  pound,  corresponds  to 
that  noted  for  some  varieties  of  dried  fruits.  It  is  practically  75  per 
cent  of  the  fuel  value  of  the  cereals  and  far  in  excess  of  the  fuel  value 
of  lean  meat. 

DIGESTIBILITY 

Digestion  experiments  conducted  by  Mattill15  have  shown  that  the 
digestion  coefficient  for  avocado  fat  for  man  is  93.8,  which  is  identical 
with  the  average  obtained  by  Drs.  Langworthy  and  Holmes  in  con- 
nection with  the  digestibility  of  butter  fat  by  man.  In  other  words, 
the  digestibility  of  avocado  fat  is  on  a  par  with  butterfat. 

There  have,  however,  been  no  metabolism  experiments  carried  on 
in  connection  with  the  protein  and  carbohydrates  of  the  avocado,  yet 
it  is  only  fair  to  assume  that  this  fruit  is  as  easily  digested  as  many 
others  whose  coefficients  have  been  determined.  The  availability  of 
the  fats  and  mineral  matter  are  fully  equal  to  that  obtained  for  the 
mixed  diet;  and  the  digestion  coefficients  of  the  carbohydrates  com- 
pare very  favorably  with  the  corresponding  figures  for  other  foods, 
but  the  availability  of  the  protein  is  appreciably  lower. 


VITAMINS 

Dr.  Santos16  has  shown  that  the  avocado  is  an  excellent  source  of 
vitamin  B  or  the  antineuritic  vitamin.  He  found  that  one-half  gram 
of  the  avocado  as  a  daily  supplement  to  the  standard  vitamin  B  free 
diet,  caused  a  recovery  in  the  weight  of  rats  which  has  been  declining 
because  of  lack  of  this  accessory  food  factor. 

Studies  are  now  in  progress  by  the  Nutrition  Division  for  the 
purpose  of  ascertaining  the  content  of  vitamin  C  in  the  avocado.  This 
fruit  is  eaten  row  and  therefore  if  it  proves  to  be  high  in  vitamin  C, 
its  nutritional  value  will  be  greatly  enhanced.  There  are  many  fruits 
and  foods  which  contain  appreciable  amounts  of  vitamin  C  in  the  raw 
stage  but  which  have  to  be  processed  or  cooked  before  ready  for  con- 

15  Mattill,  H.  A.  The  digestibility  of  the  fat  of  the  avocado.  California 
Avocado  Association  Annual  Eeport  1916:  93-95.     1917. 

16  Santos,  Francisco  O.  Some  plant  sources  of  vitamins  B  and  C.  Amer. 
Jour..  Physiology  59:  310-334.     1922. 


78  UNIVERSITY  OP  CALIFORNIA EXPERIMENT  STATION 

sumption,  resulting  in  a  great  lowering  of  the  potency  of  the  anti- 
scorbutic vitamin.  In  some  instances,  cooking  or  processing  is  entirely 
destructive  to  this  accessory  food  factor. 


DIETETIC  VALUE 

The  dietetic  value  of  fruit,  aside  from  the  actual  nutrients  which 
it  contains,  lies  in  its  succulency,  its  minerals,  its  vitamins,  and  its 
organic  acids.  If  gauged  by  its  nutritive  value  alone,  fruit  would 
seem  to  be  an  expensive  form  of  nourishment,  but  when  its  hygienic 
qualities  are  considered  its  money  value  to  the  consumer  is  difficult 
to  estimate.  Some  fruits  carry  more  nourishment  with  their  hygienic 
properties  than  others.  Some  contain  minerals  which  are  more  valu- 
able to  the  system  or  less  commonly  distributed  than  others.  Again, 
there  are  the  citrus  fruits  which  are  rich  in  vitamin  C.  Therefore, 
while  there  are  general  properties  which  are  common  to  all  fruits,  each 
has  special  properties  which  justify  individual  consideration. 

While  the  special  dietetic  value  of  a  food  can  not  always  be  forecast 
by  the  chemical  analysis,  it  is  certainly  permissible  to  suggest  the 
possibilities  which  are  indicated  by  the  results  of  such  investigation. 
It  is  always  necessary  that  such  theory  be  confirmed  by  clinical 
experience. 

Judging  from  its  composition,  the  avocado  should  perhaps  prove 
to  have  laxative  qualities  of  a  peculiar  or  individual  type,  possessing 
as  it  does  the  combination  of  the  usual  " fruit  principles,"  and  that 
of  fat  or  oil.  The  laxative  properties  of  most  fruits  depend  upon  the 
stimulating  effects  of  the  fiber  upon  the  wall  of  the  intestine  and 
partly  upon  the  organic  acids  and  minerals.  Oil  has  a  tendency  to 
soothe  and  to  lubricate  the  intestine  even  while  it  acts  as  a  mild  laxa- 
tive. The  avocado  is  a  natural  combination  of  these  two  types  of 
foods — as  if  fruit  and  olive  oil  had  been  chemically  combined  by 
nature.  Whether  or  not  there  is  any  special  advantage  in  this  natural 
combination  over  that  made  by  a  proper  selection  of  foods  remains 
to  be  proved.  There  are  no  clinical  data  on  the  subject,  but  future 
experimental  work  may  furnish  some  interesting  results. 

The  fact  that  the  native  Cubans  prefer  this  fruit  to  any  other  of 
their  abundant  supply  may  be  due  to  its  flavor  alone,  but  it  is  more 
than  likely  that  the  preference  has  a  deeper  foundation  and  that  it 
is  the  result  of  generations  of  experience  or  knowledge  of  its  beneficial 
effects. 


SELECTED    READING    LIST    FOR    AVOCADO    GROWERS 

Calavo  Growers  of  California. 

1927-1928.     The  Calavo  News   (a  journal  devoted  to  avocado  culture  in  Cali- 
fornia).    Monthly  issues.     The  Calavo  Growers  of  California,  1405 
East  Eighth  Street,  Los  Angeles. 
California  Avocado  Association. 

1915-1927.     Annual  Eeports  of  the  California  Avocado  Association. 
Church,  C.  G.,  and  E.  M.  Chace. 

1922.  Some  changes  in  the  composition  of  California  avocados  during  growth. 

U.  S.  Dept.  Agr.  Dept.  Bui.  1073:  1-22.     1  fig.     6  tables. 
Collins,  G.  N. 

1905.     The  avocado — a  salad  fruit  from  the  tropics.     U.  S.  Dept.  Agr.  Bur. 
Plant  Indus.  Bui.  77:  1-49.     8  plates. 
Condit,  I.  J. 

1926.     Check    list    of    avocado    varieties.      Beprint    from    California    Avocado 
Association  Annual  Beport  1925-1926.     20  p. 
Griffiths,  J.  P. 

1923.  The   avocado  in   Porto   Bico.     Porto   Bico   Dept.   Agr.   and   Labor   Cir. 

72:  1-41.     13  figs. 
Higgins,  J.  E.,  C.  J.  Hunn,  and  V.  S.  Holt. 

1911.     The  avocado  in  Hawaii.    Hawaii  Agr.  Exp.  Sta.  Bui.  25:  1-48.    13  figs. 
7  plates. 
Moznette,  G.  F. 

1922.     The  avocado:   its  insect  enemies  and  how  to  combat  them.     U.  S.  Dept. 
Agr.  Farmers'  Bui.  1261:  1-32.     21  figs. 
Pope,  W.  T. 

1924.  The    Guatemalan    avocado    in    Hawaii.      Hawaii    Agr.    Exp.    Sta.    Bui. 

51:  1-24.     10  plates. 
Popenoe,  Wilson. 

1919.  The  avocado  in  Guatemala.     U.   S.   Dept.   Agr.  Dept.  Bui.  743:  1-69. 

23  plates. 
Popenoe,  Wilson. 

1920.  Manual  of  tropical  and  subtropical  plants.     78  pp.     9  figs.     4  plates. 
Bobinson,  T.  Balph. 

1925.  Avocado    culture    in    Florida.-      U.    S.    Dept.    Agr.    Bur.    Plant    Indus. 

mimeo.  cir.     13  pp. 
Bobinson,  T.  Balph,  and  E.  M.  Savage. 

1926.  Pollination  of  the  avocado.     U.  S.  Dept.  Agr.  Dept.  Cir.  387:  1—16. 
Bolfs,  P.  H. 

1905.  The   avocado   in   Florida.      U.   S.   Dept.   Agr.    Bur.    Plant    Indus.    Bui. 

61:  1:35.     9  figs.     4  plates. 
Stevens,  H.  E. 

1922.     Avocado  diseases.     Florida  Agr.  Exp.  Sta.  Bui.  161:  1-23.. 
Taylor,  W.  A. 

1906.  Trapp  avocado.     U.  S.  Dept.  Agr.  Yearbook  1905:  1-815.      (p.  508.) 
Taylor,  W.  A. 

1907.  Chappelow  avocado.    U.  S.  Dept.  Agr.  Yearbook  1906:  1-720.    (p.  363.) 
Variety  Committee  of  the  California  Avocado  Association. 

1927.  Beport    of    the    Variety    Committee.     Beprint     from    the     California 

Avocado  Association  Annual  Beport  1926-1927.     8  pp. 


"'■  F'y^RAL  LIBRARY 


12//*-.        9 


THE   NUTRITIVE   VALUE  OF  THE 
AVOCADO 

t 


BY 
M.  E.JAFFA  and  H.  GOSS 


630  UNIVERSITY  OF  CALIFORNIA EXPERIMENT  STATION 


Part  II 
THE  NUTRITIVE  VALUE  OF  THE  AVOCADO* 

BY 

M.  E.  JAFFA  and  H.  GOSS 


The  investigation  here  reported  includes  110  analyses  representing 
68  different  varieties  of  the  avocado.  These  data  emphasize  the  value 
of  this  fruit  as  an  excellent  source  of  easily  digested  vegetable  fat. 

THE  AVEEAGE  COMPOSITION  OF  FKESH  FEUITS 

A  reference  to  the  composition  of  fresh  fruit  in  general  shows 
that  the  amount  of  water  is  large,  averaging  about  83  per  cent,  and 
that  the  percentage  of  the  nutrients  indicates  that  the  main  food 
value  is  derived  from  carbohydrates.  In  nearly  all  cases  sugars  pre- 
dominate, starch  being  present  in  small  amounts  only. 

The  protein  content  of  fruits  is  low,  averaging  for  the  loquat  about 
0.2  of  one  per  cent ;  apples  and  pears,  0.4-0.5  per  cent ;  fresh  prunes, 
0.9  per  cent;  melons,  0.5  per  cent;  berries,  1-1.3  per  cent;  oranges, 
0.8-1.0  per  cent ;  grapes  and  bananas,  1.2-1.5  per  cent.  The  average, 
therefore,  for  protein  for  the  fresh  fruits  enumerated  is  practically 
0.72  per  cent.    The  olive  contains  approximately  2.5  per  cent  protein. 

The  per  cents  for  the  mineral  matter  or  ash  in  fresh  fruits  are  as 
follows:  apples  and  pears,  0.3-0.4;  grapes,  0.5;  figs.  0.6;  berries,  0.6; 
oranges,  0.5 ;  melons,  0.5 ;  fresh  prunes,  0.6  ;  bananas,  1.0.  The  average 
being  0.55  per  cent,  while  the  corresponding  figure  for  meat  is  about 
1  per  cent. 

It  must  not  be  forgotten,  however,  that  while  the  amount  of  ash  is 
small,  the  percentage  of  potassium  in  the  ash  is  high.  This  is  a  very 
valuable  base-forming  element  which  is  necessary  in  the  maintenance 
of  the  normal  neutrality  of  the  blood  and  tissues.  The  importance 
of  the  mineral  matter  in  nutrition  and  the  necessity  of  carefully 
selecting  the  dietary  so  as  to  secure  a  proper  balance  between  the  base- 
forming  and  acid-forming  elements  is  becoming  more  and  more 
apparent. 


*  Credit  is  due  to  Miss  Mattie  E.  Stover  and  F.  W.  Albro  for  assistance  in 
chemical  work  incidental  to  this  investigation. 


Bulletin  365]  AVOCADO  CULTURE  IN  CALIFORNIA  631 

Fat  is  present  in  very  small  proportions  in  fresh  fruits.  This 
constituent  is  generally  reported  as  ''ether  extract"  which  often  con- 
tains other  materials  than  the  true  fats  or  oil,  such  as  coloring  matter, 
wax  found  in  the  skin,  etc.  The  figure  reported  for  fat  in  most  fruits, 
therefore,  is  seldom  a  true  indication  of  the  content  of  this  nutrient. 

Fruits  are  important  sources  of  water-soluble  vitamins.  Par- 
ticularly is  this  true  of  the  citrus  fruits  which  are  rich  in  vitamin 
C.  The  deciduous  fruits  show  appreciable  percentages  of  B  and 
berries,  like  raspberries  and  strawberries,  show  also  a  high  content  of 
vitamin  C. 

Mature  California  grown  fruits  only  are  included  in  above  tabu- 
lation. 

COMPOSITION  OF  THE  AVOCADO 

A  survey  of  the  data  presented  in  the  accompanying  tables  shows 
the  avocado  to  differ  widely  in  many  respects  from  the  average  for 
fresh  fruits  and  proves  it  worthy  of  special  consideration.  It  might 
well  be  said  to  be  in  a  class  by  itself. 

The  tables  are  replete  with  interesting  points,  all  very  favorable 
to  the  avocado.  The  total  dry  matter  in  the  edible  portion  is,  in 
nearly  every  instance,  greater  than  that  noted  for  any  other  fresh 
fruit.  The  average  for  the  avocado,  based  on  examination  of  mature 
California  fruits  is  29.44  per  cent.  The  nearest  approach  to  this 
figure  is  found  in  the  banana  with  about  25  per  cent  dry  matter.  It 
must  be  remembered,  however,  that  while  there  may  not  be  so  much 
difference  in  the  total  amount  of  solids  of  the  two  fruits  in  question, 
there  is  a  great  difference  in  the  nature  of  the  nutrients.  Sugar  and 
starch  predominate  in  the  banana  as  against  fat  in  the  avocado. 

It  has  been  stated  that  the  protein  percent  in  all  fruits  is  low, 
averaging  less  than  one  per  cent.  It  will  be  seen  from  the  table  that 
the  minimum  figure  for  protein  in  the  avocado  is  1.14,  which  is  about 
75  per  cent  of  the  maximum,  1.5  per  cent,  noted  for  figs  and  currants. 
The  maximum,  4.39  per  cent,  credited  to  Bartley  avocado  grown  at 
Santa  Ana,  corresponds  to  the  protein  content  of  some  dried  fruits. 

It  is  of  interest  in  passing  to  note  that  a  sample  of  the  Lyon  variety 
analyzed  by  the  U.  S.  Department  of  Agriculture  also  shows  the  same 
figure,  4.39  per  cent,  as  the  maximum  for  the  protein  for  this  variety. 

In  seven  of  the  varieties  the  protein  is  in  excess  of  3  per  cent ;  in 
36  varieties  between  2  and  3  per  cent ;  while  the  average  for  83  mature 
varieties  is  2.10  per  cent. 

It  therefore  may  be  said  that  so  far  as  protein  in  fresh  fruits  is 
concerned,  the  avocado  stands  in  the  lead. 


632 


UNIVERSITY  OF  CALIFORNIA EXPERIMENT  STATION 


TABLE  1. — Showing  the  Composition  of  the  Avocado 


Variety 


Locality 


10. 
11. 
12. 
13. 
14. 
15. 

16. 
17. 
18. 
19. 
20. 
21. 
22. 
23. 
24. 
25. 
26. 

27. 
28. 
29. 

30. 
31. 
32. 
33. 
34. 
35. 

36. 

37. 
38. 

39. 
40. 
41. 
42. 
43. 

44. 
45. 
46. 
47. 

48. 


Azusa Azusa 

Azusa Azusa 

Average  Azusa 

Bartley Santa  Ana.. 

Beauty Orange 

Benik Duarte 

Blake Pasadena- 
Blake Whittier 

Blakeman Altadena.... 

Blakeman Altadena. . . . 


Weight 
of 

fruit 
grams 

198 
169 
184 
928 
426 
518 
150 
120 
472 
454 


Edible  Portion 


Average  Blakeman 463 


Brodia Orange. 

Cabnal Duarte.. 

Cantel Duarte.. 

Cardinal Florida. 

Caribou Duarte.. 

Caribou Duarte.. 


405 
459 
351 

587 
464 
486 

Average  Caribou 475 

Carmen Altadena 139 

Carton San  Fernando 169 

Carton* Riverside 108 

Challenge* Hollywood 1060 

Challenge Hollywood 669 

Champion Orange 506 

Chappelow Monrovia 181 

Chappelow Monrovia 173 

Chappelow Monrovia 104 

Chappelow Monrovia 110 

159 
145 
80 
143 
150 
146 
363 
560 
254 
132 
315 
566 
440 
254 
270 
256 
263 
205 
197 
127 
136 
170 
144 
235 
263 
233 
215 
192 


Chappelow Monrovia 

Average  Chappelow 

Chappelow* Altadena 

Condon Pasadena 

Condon Pasadena 

Average  Condon 

Dickey Hollywood 

Dickey* Nordhoff 

Dickinson Puente 

Fowler Pasadena 

Fuerte Yorba  Linda... 

Fuerte Yorba  Linda... 

Average  Fuerte 

Fuerte* Yorba  Linda... 

Fuerte Altadena 

Fuerte Altadena 

Average  Fuerte 

Ganter Whittier 

Ganter* Whittier 

Harman* Sherman 

Harman* Sherman 

Harman* Sherman 

Average  Harman* 

Harman Sherman 

Harman Sherman 

Harman Sherman 

Harman Sherman 

Harman Sherman 

Average  Harman  mature 227 

Immature. 


Refuse 
per  cent 

28.30 
13.60 
21.00 
21.33 
34.07 
31.06 
32.66 
31.60 
30.30 
20.81 
25.57 
36.80 
33.11 
24.79 
19.00 
31.04 
19.80 
25.42 
31.30 
41.20 
26.06 
40.57 
17.78 
30.00 
22.43 
31.00 
36.34 
36.90 
23.30 
29.99 
30.30 
34.20 
24.00 
29.10 
30.00 
24.55 
29.99 
35.80 
25.71 
26.14 
25.92 
23.62 
26.48 
28.71 
27.59 
16.60 
26.80 
35.50 
37.90 
37.40 
36.93 
46.38 
34.70 
33.50 
34.90 
28.00 
41.61 


Water 
per  cent 

67.05 
62.69 
64.87 
77.12 
72.68 
69.98 
65.76 
68.24 
74.33 
77.72 
76.87 
80.80 
67.15 
72.04 
79.66 
82.31 
79.02 
80.66 
63.39 
70.43 
78.32 
79.61 
76.23 
74.32 
60.94 
63.58 
63.74 
58.99 
70.77 
63.61 
75.34 
69.11 
70.30 
69.70 
60.50 
81.10 
72.04 
70.33 
66.30 
68.32 
67.31 
80.88 
65.26 
65.67 
65.46 
63.86 
77.87 
75.17 
76.09 
75.42 
75.56 
71.58 
74.70 
72.05 
73.44 
72.75 
72.90 


Protein 
per  cent 

1.94 
2.91 
2.43 
4.39 
2.48 
1.97 
1.88 
1.81 
2.61 
3.15 
2.88 
1.26 
2.08 
2.43 
2.56 
1.34 
2.21 
1.77 
1.22 
2.60 
1.38 
3.43 
2.81 
2.59 
1.40 
2.63 
2.19 
2.79 
2.25 
2.25 
2.30 
2.50 
1.31 
1.91 
2.20 
2.01 
1.56 
1.60 
1.42 
1.36 
1.39 
1.04 
1.40 
1.51 
1.46 
2.25 
2.13 
1.69 
1.24 
1.47 
1.47 
2.50 
1.60 
1.43 
1.14 
1.16 
1.57 


Fat 
per  cent 

21.06 
26.44 
23.75 
13.35 
15.26 
22.02 
25.50 
21.65 
17.27 
15.43 
16.35 
10.88 
23.71 
19.00 
10.70 
10.33 
12.00 
11.17 
26.38 
19.50 
12.71 
13.14 
16.37 
16.54 
29.10 
24.43 
22.81 
27.65 
20.28 
24.85 
14.66 
21.00 
23.55 
22.28 
27.11 
11.81 
20.36 
21.20 
25.32 
24.23 
24.77 
11.61 
28.68 
26.60 
27.64 
25.60 
16.48 
15.25 
15.34 
16.26 
15.62 
19.33 
18.30 
21.51 
18.68 
19.18 
19.40 


Carbo- 
hydrates 
per  cent 

8.59 
6.15 
7.37 
3.74 
8.22 
4.42 
5.52 
8.18 
4.94 
2.59 
3.76 
6.30 
5.69 
4.90 
6.48 
4.60 
5.43 
5.02 
7.46 
6.29 
6.60 
2.62 
3.05 
5.31 
6.85 
8.06 
10.00 
9.33 
5.13 
7.88 


6.73 

3.62 

5.17 

8.76 

3.75 

4.69 

5.61 

5.68 

4.82 

5.25 

5.53 

3.22 

4.62 

3.92 

6.58 

2.48 

7.00 

6.65 

5.86 

6.50 

32 

61 

21 

17 

86 

03 


Ash 
per  cent 

1.36 
1.81 
1.58 
1.40 
1.36 
1.61 
1.34 
1.12 
0.85 
1.11 
0.98 
0.76 
1.37 
1.59 
0.60 
1.42 
1.34 
1.38 
1.55 
1.18 
0.99 
1.20 
1.54 
1.24 
1.71 
1.30 
1.26 
1.23 
1.57 
1.41 
0.90 
0.66 
1.22 
0.94 
1.43 
1.33 
1.35 
1.26 
1.28 
1.27 
1.28 
0.94 
1.44 
1.63 
1.52 
1.71 
1.04 
0.89 
0.68 
0.99 
0.85 
1.27 
0.80 
0.77 
1.57 
1.05 
1.10 


Bulletin  365] 


AVOCADO  CULTURE  IN   CALIFORNIA 


633 


TABLE   1. — (Continued) 


Variety 


Locality 


70. 

71. 
72. 

73. 

74. 
75. 
7G. 
77. 
78. 
79. 
80. 
81. 
82. 
83. 
84. 
85. 


87. 


I.  X.  L  * Duarte 

I.  X.  L Duarte 

Kist Yorba  Linda. 

Kist Yorba  Linda. 

Average  Kist 

Lamat Duarte 

Lambert Hollywood 

Lyon Hollywood 

Lyon La  Habra 

Mattern Unknown 

Mayapan Duarte 

Mayapan Duarte 


Weight 

of 

fruit 

grams 

705 
800 
456 
478 
467 
332 
285 
453 
453 
92 
397 
449 


Edible  Portion 


Average  Mayapan 423 

Meserve Puente 331 

Miller Hollywood 184 

Miller Pasadena 275 

Monrovia Altadena 166 

Nimlich Duarte 860 

Northrup Santa  Ana 164 

Pankay Duarte 385 

Pankay Duarte 310 

Average  Pankay 347 

Pomona Sacramento 79 

Popenoe  101 Altadena 327 

Popenoe  101 Altadena 375 

Average  Popenoe  101 346 

Puebla* Altadena 168 

Puebla Altadena 280 

Puebla Altadena 158 

Average  Puebla  mature 219 

Purdy Whittier 168 

Purple  Prolific  ....Orange 219 

Queen Unknown 663 

Queretaro Yorba  Linda 217 

Queretaro Altadena 164 

Rhoad Orange 395 

Rita* Orange 321 

Royal Hollywood 600 

Royal  Purple San  Diego 200 

Senor Orange 528 

Sharpless* Santa  Ana 471 


Sharpless* Santa  Ana.. 

Average  Sharpless* 

Sharpless Santa  Ana.. 

Sharpless Santa  Ana.. 

Average  Sharpless 

Sinaloa Whittier 

Spinks Duarte 

Spinks Duarte 

Average  Spinks 

Surprise Hollywood. 

Taft Orange 

Taft* Orange 

Taft* Orange 


555 
513 
594 
536 
565 
616 
388 
877 
633 
538 
626 
417 
296 
Average  Taft* 356 


Refuse 
per  cent 

31.60 
23.00 
31.35 
28.20 
29.77 
30.42 
33.40 

26.50 
44.00 
37.28 
28.06 
32.67 
40.00 
35.80 
40.00 
37.00 
24.42 
34.70 
41.30 
46.12 
43.76 
43.00 
23.82 
29.34 
26.58 
34.00 
27.50 
36.00 
31.75 
32.10 
45.90 
29.15 
37.80 
36.60 
37.00 
42.68 
26.33 
26.00 
21.00 
21.23 
22.50 
21.86 
23.10 
24.10 
23.65 
23.40 
31.50 
20.30 
25.90 
26.00 
29.00 
25.00 
27.00 
26.00 


Water 
per  cent 

84.27 
78.12 
76.84 
74.71 
75.78 
77.32 
76.52 
75.78 
74.80 
61.55 
68.33 
70.26 
69.29 
74.66 
66.60 
63.68 
64.18 
78.55 
66.31 
73.15 
71.03 
72.09 
61.84 
58.71 
60.78 
59.74 
80.59 
69.47 
67.53 
68.50 
60.28 
69.30 
73.80 
71.46 
71.46 
82.46 
71.05 
76.34 
72.96 
74.70 
76.73 
75.33 
76.03 
71.21. 
72.63 
71.92 
73.55 
76.22 
75.72 
75.97 
82.51 
72.53 
76.11 
77.25 
76.68 


Protein 
per  cent 

2.12 

2.17 
1.51 
2.41 
1.96 
1.42 
2.86 
2.48 
2.76 
2.20 
1.77 
2.25 
2.01 
2.19 
3.70 
3.36 
2.09 
1.53 
2.36 
1.58 
1.64 
1.61 
3.50 
2.39 
1.82 
1.65 
1.76 
1.66 
1.83 
1.74 
1.14 
1.67 
2.21 
2.85 
2.34 
1.19 
1.57 
1.39 
1.72 
1.69 
2.15 
3.06 
2.60 
1.70 
1.27 
1.48 
2.67 
1.50 
2.10 
1.80 
1.90 
2.66 
2.30 
3.44 
2.87 


Fat 
per  cent 

7.50 
13.47 
12.16 
14.92 
13.54 
14.29 
14.31 
16.31 
15.58 
25.70 
22.83 
21.80 
22.32 
17.01 
23.70 
27.45 
25.34 
13.93 
23.00 
14.56 
16.30 
15.43 
25.36 
31.59 
29.78 
30.68 
11.32 
20.94 
26.14 
23.54 
31.60 
19.93 
16.35 
17.45 
18.21 

9.78 
14.13 
15.61 
19.39 
17.03 
15.73 
15.87 
15.80 
20.54 
18.77 
19.65 
16.43 
14.83 
16.01 
15.42 

9.96 
18.54 
14.67 
12.59 
13.63 


Carbo 
hydrates 
per  cent 

4.70 
4.74 
8.13 
6.49 
7.31 
5.57 
5.40 
4.38 
6.01 
8.94 
5.59 
4.13 
2.86 
4.78 
4.51 
4.18 
6.73 
4.83 
7.12 
9.10 
9.61 
9.36 
7.36 
5.65 
5.92 
5.78 
5.22 
6.65 
3.16 
4.91 
5.49 
8.27 
6.01 
6.79 
6.56 
6.03 
12.25 
5.97 
4.84 
5.45 
3.69 
4.52 
4.11 
5.43 
6.39 
5.91 
5.57 
5.96 
4.74 
5.35 
4.86 
5.16 
6.00 
4.91 
5.45 


Ash 
per  cent 

1.41 
1.50 
1.36 
1.47 
1.41 
1.40 
0.91 
1.05 
0.85 
1.61 
1.48 
1.56 
1.52 
1.36 
1.49 
1.33 
1.66 
1.16 
1.21 
1.61 
1.42 
1.51 
1.94 
1.66 
1.70 
1.68 
1.11 
1.28 
1.34 
1.31 
1.49 
0.83 
1.63 
1.45 
1.43 
0.54 
1.00 
0.69 
1.09 
1.13 
1.70 
1.22 
1.16 
1.12 
0.94 
1.03 
1.78 
1.49 
1.43 
1.46 
0.77 
1.11 
0.92 
1.81 
1.37 


*  Immature. 


634 


UNIVERSITY  OF  CALIFORNIA EXPERIMENT  STATION 


TABLE   1.— (Continued) 


Variety 


Locality 


95.  Topa  Topa Nordhoff 

96.  Trapp Florida 

97.  Ultimate Orange 

98.  Walker Sherman 

99.  Wagner Hollywood 

100.  Dr.  Weldon Duarte 

101.  W.  I.  G Altadena 

102.  White Santa  Barbara. 


No.  of 


Edible  Portion 


Weight 

of 

fruit 

grams 

123 

638 
277 
174 
259 
450 
123 
162 

Weight 

of 

fruit 


Carbo- 
Refuse      Water     Protein       Fat      hydrates       Ash 
per  cent  per  cent  per  cent  per  cent  per  cent  per  cent 


27.70 
28.50 
37.40 
37.10 
47.00 
41.00 
28.50 


75.00 
78.66 
75.01 
68.66 
74.84 
63.75 
60.00 


2.30 
1.61 
1.57 
3.15 

2.77 
2.57 
2.63 


15.48 
9.80 
14.51 
18.71 
16.03 
24.29 
26.73 


35.00       77.06       1.74 


Refuse     Water     Protein 


6.14 
9.08 
4.88 
7.55 
5.05 
7.79 
9.08 
14.64       5.49 


1.08 
0.85 
1.03 
1.93 
1.30 
1.60 
1.56 
1.07 


Fat 


Carbo- 
hydrates      Ash 


Analyses    grams     per  cent  per  cent  per  cent   per  cent  per  cent  per  cent 


Maximum. 
Minimum.. 
Average.... 


928 

79 

347 


47.00 
13.60 
32.11 


82.31 
58.71 
70.56 


4.39 
1.14 
2.10 


31.60 

9.78 

20.06 


10.00  1.94 

2.59  0.54 

5.95  1.32 


Mature  California  grown  fruits  only  are  included  in  above  tabulation. 


Variety 


Partial  Analyses 

Weight 

of  fruit 

Locality  grams 


1.  Atlixco Yorba  Linda.. 

2.  Atlixco Yorba  Linda... 

Average  Atlixco 

3.  Goldie San  Diego 

4.  Knight Yorba  Linda.. 

5.  Linda Unknown 

6.  Snell Sierra  Madre. 

7.  Tahiti San  Diego 

8.  Whittier Whittier 


352 
532 
442 
165 
570 
890 
306 
256 
687 


Refuse 
per  cent 

26.52 
26.86 
26.69 
35.50 
26.95 
20.23 
29.00 
19.50 
23.00 


Water 
per  cent 

63.70 
63.10 
63.40 
56.50 
71.03 
82.66 
55.00 
50.60 
75.20 


Fat 
per  cent 

28.80 
26.90 
27.95 
26.67 
23.31 
7.48 
32.70 
23.20 
21.20 


The  carbohydrate  content  of  the  avocado  is  low  as  compared  with 
this  constituent  in  fresh  fruits.  The  average  for  the  83  mature 
varieties  is  5.95  per  cent,  with  a  maximum  of  10  per  cent  and  a 
minimum  of  2.59  per  cent. 

The  figures  quoted  in  the  table  for  carbohydrates  include  crude 
fiber  which  was  not  determined  in  every  case.  Analyses  of  a  number 
of  samples  have  shown,  however,  that  this  ingredient  would  average 
about  1.5  per  cent,  which  compares  very  favorably  with  the  content 
of  crude  fiber  in  other  fresh  fruits. 

It  is  of  decided  interest  to  note  that  the  percentage  of  mineral 
matter  in  the  avocado  is  much  higher  than  that  recorded  for  any  other 
fresh  fruit.  The  minimum  0.54  per  cent,  reported  for  the  Rhoad 
variety,  equals  approximately  the  average  for  most  of  our  fresh  fruits, 
while  the  average  for  the  avocado,  1.32  per  cent,  shows  that  it  contains 
twice  as  much  mineral  matter  as  that  yielded  by  any  other  fruit. 


Bulletin  365]  AVOCADO  CULTURE  IN  CALIFORNIA  635 

The  following  analysis  of  the  ash  of  the  avocado  shows  that,  like 
other  fruit,  the  avocado  yields  an  excess  of  the  base-forming  elements : 

Silica  0.50 

Phosphoric   acid   17.40 

Lime    4.72 

Magnesia    5.30 

Iron   1.51 

Aluminum     2.58 

Manganese Trace 

Sulfuric   Acid    11  24 

Chlorin    14.36 

Potash  26.23 

Soda    18.55 

101.89 
Oxygen  equivalent  to  chlorin  2.09 

99.80 

Nearly  one-half  of  the  ash  consists  of  soda  and  potash,  the  latter 
predominating.  Magnesia  and  lime  occur  in  comparatively  small 
amounts,  about  5  per  cent  each;  the  phosphoric  acid  averaging  about 

17.5  per  cent,  with  1.5  per  cent  of  iron. 

The  foregoing  discussion  clearly  indicates  that  so  far  as  protein 
and  ash  in  fresh  fruits  are  concerned,  the  avocado  stands  at  the  head 
of  the  list,  and,  with  reference  to  the  carbohydrates,  contains  on  an 
average  fully  50  per  cent  of  that  found  in  many  fresh  fruits.  These 
facts  alone  would  warrant  due  consideration  of  the  value  of  the 
avocado  as  a  fresh  fruit. 

The  chief  value  of  the  avocado  as  food,  however,  is  due  to  its  high 
content  of  fat.  This  varies,  as  shown  by  the  analyses,  from  a  minimum 
of  9.78  per  cent  to  a  maximum  of  31.6  per  cent,  with  an  average  of 

20.6  per  cent. 

Reviewing  the  analytical  data,  it  will  be  seen  that  15  varieties 
show  more  than  25  per  cent  fat  and  14  other  varieties  an  excess  of 
20  per  cent.  The  only  fruit  comparable  with  the  avocado  in  this 
respect  is  the  olive.  In  this  connection,  it  is  of  interest  to  note  the 
comparison  as  shown  in  the  following  table,  of  the  fat  percentages  of 
the  edible  portion  of  ten  varieties  of  the  avocado  containing  25  per 
cent  or  more  of  fat,  with  ten  varieties  of  the  olive. 


636 


UNIVERSITY  OF  CALIFORNIA EXPERIMENT  STATION 


TABLE  2. — Showing  Percentage  of  Fat  or  Oil  in  the  Avacado  and  Olive 

Olive — Edible  Portion 

Original  Material 

Oil 
Variety  per  ct. 

Corregiolo    27.68 

Nigerina  26.16 

Nevadillo   Blanco  ....  22.92 

Mission  22.51 

Rubra   22.01 

Pendulina    21.36 

Redding  Picholine....  20.83 

Macrocarpa   20.41 

Manzanillo     19.73 

Columbella  19.54 


Avocado — Edible  Portion 

Original  Material     Wat< 

er-Free 

Water 

Fat 

Fat 

Variety 

per  ct. 

per  ct. 

per  ct. 

Purdy  

60.28 

31.60 

79.70 

Popenoe  . 

59.74 

30.68 

76.20 

Ghappelow    60.94 

29.10 

74.40 

Fuerte  ... 

65.26 

28.68 

82.50 

Miller 

63.68 

27.45 

75.60 

Dickey  ... 

60.50 

27.11 

68.70 

A.zusa 

62.69 

26.44 

70.90 

Carmen   . 

63.39 

26.38 

72.10 

Ganter  ... 

63.86 

25.60 

70.80 

Blake  

65.76 

25.50 

74.50 

The  figures  in  table  2  indicate  that  the  avocado  ranks  higher  in 
fat  or  oil  than  the  average  or  commonly  used  olive.  The  olive  also 
has  the  disadvantage  of  requiring  special  treatment  before  it  is  ready 
for  consumption  and  should  really  rank  as  a  processed  fruit  rather 
than  a  fresh  one.  The  data  in  the  table  show  that,  when  considering 
the  dry  matter  only,  the  Purdy  has  the  highest  per  centage  of  fat. 
In  the  original  condition,  the  Blake  and  the  Chappelow  differ  in  fat  by 
nearly  4  per  cent,  which  difference  is  practically  eliminated  when  com- 
parison is  made  on  a  water-free  basis,  which  is  the  only  true  way  to 
compare  the  nutritive  value  of  fruits. 

CALORIC  VALUE 

While  it  is  true  that  the  real  value  of  any  food  is  not  always  rep- 
resented by  the  heat  units  or  calories,  at  the  same  time,  the  total  food 
value  is  so  indicated.  This  difference  between  the  real  food  value 
and  the  total  food  value  is  not  always  properly  understood.  For 
instance,  the  energy  value  of  a  pound  of  sugar  is  1820  calories,  while 
the  corresponding  value  for  lean  meat  is  less  than  1000  calories.  Yet 
we  would  hardly  say  that  the  real  value  of  a  pound  of  sugar  was  1.8 
times  that  of  a  pound  of  lean  meat,  if  the  question  of  growth  were 
under  consideration.  When,  however,  the  matter  of  energy  is  being 
discussed  the  case  is  entirely  different,  and  the  value  of  a  food  as  a 
source  of  energy  varies  directly  with  its  caloric  value. 

The  energy  values  of  the  edible  portion  of  the  commonly  used 
fresh  fruits  are  low,  ranging  from  a  minimum  of  175  calories  to  a 
possible  maximum  of  400  calories  per  pound. 

An  inspection  of  table  3  shows  that  the  avocado  has  a  far  higher 
value  in  this  respect,  the  average  for  twenty  varieties,  being  1056  per 
pound,  or  more  than  twice  the  maximum    (400  calories)   noted  for 


Bulletin  365]  AVOCADO  CULTURE  IN  CALIFORNIA  637 

other  fresh  fruits.  The  minimum,  783  calories,  approaches  very 
closely  to  this  figure.  The  maximum,  1376  calories  per  pound,  cor- 
responds to  that  noted  for  some  varieties  of  dried  fruits.  It  is  prac- 
tically 75  per  cent  of  the  fuel  value  of  the  cereals  and  far  in  excess 
of  the  fuel  value  of  lean  meat. 

TABLE  3. — Showing  the  Energy  Value  of  the  Avocado 

Energy  value  Energy  value 

No.  and  per  pound  No.  and  per  pound 

variety  calories  variety  calories 

1.  Azusa    1,235            12.  Mayapan  992 

2.  Blake  1,083             13.  Miller    1,159 

3.  Blakeman  783            14.  N/orthrup  1,101 

4.  Cabnal  1,100            15.  Pomona  1,223 

5.  Chappelow    1,184             16.  Popenoe    1,376 

6.  Dickey 1,293             17.  Puebla    1,026 

7.  Dickinson   958            18.  Queen  812 

8.  Fuerte   1,187            19.  Sharpless    928 

9.  Ganter  : 1,195            20.  Sinaloa    814 


10.  Harman  904  

11.  Lyon    785  Average  1,056 

DIGESTIBILITY 

Digestion  experiments  conducted  by  Mattill12  have  shown  that  the 
digestion  coefficient  for  avocado  fat  for  man  is  93.8,  which  is  identical 
with  the  average  obtained  by  Dr.  Langworthy  and  Holmes  in  connec- 
tion with  the  digestibility  of  butter  fat  by  man.  In  other  words,  the 
digestibility  of  avocado  fat  is  on  a  par  with  butter  fat. 

There  have,  however,  been  no  metabolism  experiments  carried  on 
in  connection  with  the  protein  and  carbohydrates  of  the  avocado,  yet 
it  is  only  fair  to  assume  that  this  fruit  is  as  easily  digested  as  many 
others  whose  coefficients  have  been  determined.  Such  data  clearly 
prove  that  the  fruits  are  quite  thoroughly  digested.  The  availability 
of  the  fats  and  mineral  matter  are  fully  equal  to  that  obtained  for  the 
mixed  diet;  and  the  digestion  coefficients  of  the  carbohydrates  com- 
pare very  favorably  with  the  corresponding  figures  for  other  foods, 
but  the  availability  of  the  protein  is  appreciably  lower. 

VITAMINS 

Dr.  Santos13  has  shown  that  the  avocado  is  an  excellent  source  of 
vitamin  B  or  the  antineuritic  vitamin.  He  found  that  one-half  gram 
of  the  avocado  as  a  daily  supplement  to  the  standard  vitamin  B  free 
diet,  caused  a  recovery  in  the  weight  of  rats  which  had  been  declining 
because  of  lack  of  this  accessory  food  factor. 

Studies  are  now  in  progress  by  the  Nutrition  Division  for  the 
purpose  of  ascertaining  the  content  of  vitamin  C  in  the  avocado.    This 

12  California  Avocado  Association,  Annual  Eeport,  1916. 

13  Amer.  Jour.  Physiol.  LIX,  1922,  p.  310. 


638  UNIVERSITY  OF  CALIFORNIA EXPERIMENT  STATION 

fruit  is  eaten  raw  and  therefore  if  it  proves  to  be  high  in  vitamin  C, 
its  nutritional  value  will  be  greatly  enhanced.  There  are  many  fruits 
and  foods  which  contain  appreciable  amounts  of  vitamin  C  in  the  raw 
state  but  which  have  to  be  processed  or  cooked  before  ready  for  con- 
sumption, resulting  in  a  great  lowering  of  the  potency  of  the  anti- 
scorbutic vitamin.  In  some  instances,  cooking  or  processing  is  entirely 
destructive  to  this  accessory  food  factor. 

DIETETIC   VALUE 

The  dietetic  value  of  fruit,  aside  from  the  actual  nutrients  which 
it  contains,  lies  in  its  succulency,  its  minerals,  its  vitamins,  and  its 
organic  acids.  If  gauged  by  its  nutritive  value  alone,  fruit  would 
seem  to  be  an  expensive  form  of  nourishment,  but  when  its  hygienic 
qualities  are  considered  its  money  value  to  the  consumer  is  difficult 
to  estimate.  Some  fruits  carry  more  nourishment  with  their  hygienic 
properties  than  others.  Some  contain  minerals  which  are  more  valu- 
able to  the  system  or  less  commonly  distributed  than  others.  Again, 
there  are  the  citrus  fruits  which  are  rich  in  vitamin  C.  Therefore, 
while  there  are  general  properties  which  are  common  to  all  fruits,  each 
has  special  properties  which  justify  individual  consideration. 

While  the  special  dietetic  value  of  a  food  can  not  always  be  fore- 
cast by  the  chemical  analysis,  it  is  certainly  permissible  to  suggest 
the  possibilities  which  are  indicated  by  the  results  of  such  investiga- 
tion. It  is  always  necessary  that  such  theory  be  confirmed  by  clinical 
experience. 

Judging  from  its  composition,  the  avocado  should  perhaps  prove 
to  have  laxative  qualities  of  a  peculiar  or  individual  type,  possessing 
as  it  does  the  combination  of  the  usual  "fruit  principles,"  and  that 
of  fat  or  oil.  The  laxative  properties  of  most  fruits  depend  upon  the 
stimulating  effects  of  the  fiber  upon  the  wall  of  the  intestine  and 
partly  upon  the  organic  acids  and  minerals.  Oil  has  a  tendency  to 
soothe  and  to  lubricate  the  intestine  even  while  it  acts  as  a  mild  laxa- 
tive. The  avocado  is  a  natural  combination  of  these  two  types  of 
foods — as  if  fruit  and  olive  oil  had  been  chemically  combined  by 
nature.  Whether  or  not  there  is  any  special  advantage  in  this  natural 
combination  over  that  made  by  a  proper  selection  of  foods  remains 
to  be  proved.  There  are  no  clinical  data  on  the  subject,  but  future 
experimental  work  may  furnish  some  interesting  results. 

The  fact  that  the  native  Cubans  prefer  this  fruit  to  any  other  of 
their  abundant  supply  may  be  due  to  its  flavor  alone,  but  it  is  more 
than  likely  that  the  preference  has  a  deeper  foundation  and  that  it 
is  the  result  of  generations  of  experience  or  knowledge  of  its  beneficial 
effects. 


